Projectile motion practice problems

Name says it all:

Projectile motion practice (and solutions)


Please share other resources you find with the class through the blog.

How to study distraction free

More last minute advice:

How to study distraction free

Mr. Burk's Top 5 Places to Study in Atlanta

One more great suggestion from Study Hacks is how Adventure Studying is a great way to prepare to study.

What is adventure studying? It's finding a cool, beautiful and quiet place for you to go away and study (and adventure doesn't involve Starbucks).

Here are my top 5 suggestions in the Atlanta Area:

1. The High Museum of Art—admission is a bit pricy ($15), but the cafe across the courtyard is free, rarely crowded and a great place to sit and admire the physics of the alexander calder mobile in the front (ever wonder how it stays balanced?)

2. Chuck E Cheese. You know you loved it 5 years ago. Why not go there, work for 45 minutes and then play some skee ball to put your physics knowledge to the test? If you go, bring headphones and find a quiet corner away from all the dancing robots.

3. A local college—Agnes Scott, Morehouse, Spelman, Emory, Georgia Tech—all of these places have beautiful campuses and libraries. It can be great fun to go to a college library for the afternoon.

4. The Carter Center--Recently completely renovated, you can visit a full scale model of the Oval Office (and that's a place where you really need to understand physics--check out Physics for Future Preisdents--a real course at UC Berkeley).

5. Outside—yes, it's supposed to be a bit rainy and cold this weekend, but it it would be great bundle up, to throw some FARMIPS and and some blank paper in your backpack, and go hike to some quiet, isolated place and solve physics problems under a tree.

You need to watch this!!

Ok, if you thought today had some insane projectile motion, you need to check out this video.

Just a side note: turn up the volume on your computer and know that this is 100% genuine and was created by people somewhere and it's going into the Smithsonian soon!

Just watch: http://www.youtube.com/watch?v=KIABTxAAX90

Class last Thursday

In advance...I do not know how to get the pictures up on the post...I am sorry. If you want the pictures for that class txt me and I will give them to you.


Now then: Our began with simple note taking on energy and pie charts about energy. We learned that there are 3 kinds of energy that we use. #1 is kinetic energy. #2 is Eint, and #3 is U(insert letter here). All thease types of energy happen at different times when a ball is dropped. We then took our energy packets and each did a problem on a whiteboard for about 30 mins. After that, we presented our problems while explaining it to the class. (I will post more on this tomorrow with pictures)

how to create an online calendar for the upcoming week

I've created a google spreadsheet to help you plan out your success week to help you demonstrate your best understanding on the exam. To use it, go here

Study Plan for Finals Week

The spreadsheet is read-only, so you'll need to make a copy.

To do that, click on "File > Make a copy" as shown in the image below.

If you'd like me to see your study plan, simply share it with me via google docs (this is completely optional).

5 Mistakes to avoid during finals

Here is more great advice from study hacks:

5 mistakes to avoid during finals.

We'll talk about this a bit tomorrow, but here they are briefly

• Mistake #1: Not Having a Clear Schedule
  
  You should set up a plan for using the time you have to maximum benefit—giving yourself time to rest, and reflect so you achieve maximum understanding.
  
  
• Mistake #2: Not Purging Your Obligations
  
  Avoid letting the little things in your life keep you from having the
  time you need to seriously prepare for exams.
  
  
• Mistake #3: “Studying”
  
  Focus on specific action. Solve problems.
  
  
• Mistake #4: Social Working
  
  While it can be helpful to work with others, often, working in a noisy space with friends can be very unproductive.
  
  
• Mistake #5: Calculating Your Final Grade
  
  I'll let Cal speak for himself:
  
  

  
  Don’t do this! No good can possibly come from such a superficial focus on the numbers. It will add stress. This, in turn, will make it harder for you to execute a reasonable, specific, and efficient study plan. Also, it’s just plain crass. You don’t want to be that person…
  

  
  

Friday December 4, 2009

Today, we reviewed the packet that we were supposed to do on Wednesday. We started with Problem 6 which was Paxton and Sana's. This problem was way more complex than it looked. It is pictured in the first image, the orange one. The objects in the system are the spring the Earth and the object.. The first pie chart is entirely Ue. The second pie chart is half Ug, half K. The last pie chart is all Ug.

Problem 7, the second picture, the purple one, involved the clay and the Earth. The first chart is entirely Ug. The second is half of Ug and half K. The third is Eint, because it hit the ground.

The final problem involved the truck, the Earth, the road, and the gasoline (which is technically part of the truck). The first part is half K half Uchemical, from the gasoline. The second chart is half K, one quarter Eint, one quarter U chem. The final chart is half K, one third Eint, and one eighth Uchem.

Data

Click on the title. I think this works

Class on Tuesday December 1

The first thing that we did in class was take a reassessment on chapter 3. Then, we turned that in and continued our discussion of how different things hurt us and why. We concluded that objects can hurt us for many different reasons, including mass, velocity, displacement, and heat. We also guessed that how objects hurt us is related to energy. Then we derived an equation with displacement and acceleration in terms of final velocity and initial velocity. Then we took a break, and when we got back, Mr. Burk gave us propsicles. After the break we started on a lab. We set up a cart and a spring on a ramp, and launched the cart on the ramp with different inclines. This is what the set up looked like.

We measured many different aspects of the cart's motion as we changed theta, the angle of elevation of the ramp. Specifically, we measured the cart's maximum velocity and we measured the hight that the car traveled. We found that the height remains the same regardless of the angle. Finally we started working on the energy work packet. We discussed the types of energy that we know so far: kinetic and potential, but we can't call it potential because we don't understand what that means. That's all we did. Homework is test corrections, and the next blogger is Dylan.

Class on Monday, November 30

The first thing in class that we did was take a reassesment. Then we started talking about FARMIPS and grades and how to prepare for the exam.

We then talked about whether a bowling ball dropped from a foot above your hand or a baseball dropped from the top of robinson would hurt more if dropped on your hand. We decided that the pain and how much you'd get hurt relies on speed, mass, and height (if dropped). Then, we jumped from that subject onto springs. Let's say we have a very loose spring, and a very stiff spring. We asked ourselves "How can we launch the same cart with the same speed using these two different springs?" We made this graph of the spring force vs. the displacement:

The rest we did in class i didn't catch so we'll talk about it tomorrow! The next scribe is Joe.

Class on Tuesday

Today in class we discussed the article that we read for homework. We went over the topic of meta cognition, and a fixed mindset vs a growth mindset. A lady did an experiment that showed when they told a kid they were smart the kid opted to choose an easier test, and when someone was told that they were a hard worker they chose the harder test. For the rest of the class period we did a lab that reflected vpython, and we tried to experiment with it and learn how to use it. This class period was mostly experimental and we all went away with a basic understanding of vpython. The day before we took a major reasessment.

LHC is on!

THe LHC produced the first collisions of protons today.

Friday Nov. 20

On Friday we started by taking a chapter 4 reassessment. After we finished we got a blank copy of it and went over it. Next we broke into groups to solve a hard problem that Mr. Burk gave us. On the board Mr. Burk drew a block with mass, m. Attached to it was a spring that was angled upward at angle theta, had a stretch of change in r, and a spring constant, k. Our task was to solve for k in terms of m, theta, and the coefficient of friction. The problem was long, hard and tedious. It took a lot of steps, algebra, and combining different concepts we have learned but in the end we figured it out and I think everybody either got the answer or came within a step or two of it. Next we came back together and Mr. Burk solved the problem himself and went over the steps. After that we reviewed for our assessment on Monday. We started from 4.1 and went over each concept. That was pretty much what we did in class on Friday. Don't forget about the assessment Monday. Jason wanted to be the scribe for Monday.

what is the homework? (my email won't work and for some reason i can't type in the text box...)

Gamma Ray Satellite may have found dark matter

Here's another great post that describes a recent discovery of what may be dark matter, which makes up 20% of our universe (regular matter is only 4%).

The excess gamma rays could possibly be coming from a hypothesized dark matter called Weakly Interacting Massive Particles (WIMPs), colliding with one another and annihilating themselves into pure energy.

Fermi may have spotted dark matter.

Want to conquer stress? Exercise is key

Here's a great article from the NYT about a new study on rats showing that exercise allows our brains to better handle stress.

Here's a quote:

It looks more and more like the positive stress of exercise prepares cells and structures and pathways within the brain so that they’re more equipped to handle stress in other forms,” says Michael Hopkins, a graduate student affiliated with the Neurobiology of Learning and Memory Laboratory at Dartmouth, who has been studying how exercise differently affects thinking and emotion. “It’s pretty amazing, really, that you can get this translation from the realm of purely physical stresses to the realm of psychological stressors.

solution to conical pendulum

here's the link, via posterous. If this doesn't work, I've also posted it to the calendar.

http://john-pyicv.posterous.com/

Posterous: another super cool tool!

Have you ever wanted to share a file, mp3, photo, or video without having to email everyone, or post an elaborate facebook status? Perhaps you have some great notes you want to share on the blog.

Well, here's the solution.

Just send an email to post@posterous.com, and attach whatever it is you want to share. Posterous will send you a link to the website you created with that attachment.

It couldn't be easier.

Jujitsu Time

First off we went through simple harmonic motion and the simpleness of deriving it's formula.
Now All Questions are supposed to be answered. How does this relate to the pendulum?


@= Theta for the purposes of this

Also on Centripetal Motion:
4π^2r/T^2=a=v^2/R

We can Determine that 2π*Square Root of (L/G) = 2π*Square root of (M/K) = T.

We use the following

Determining Simple Harmonic Motion over a Pendulum
Things we can assume:
Ay=O (Basically it's not moving up and down.)
Cos@ =1 (There is minimal movement of the pendulum so the cosine of the degrees is very close to 1 because the degrees movement is really small).

The Jujitsu Way to Own a Simple Pendulum problem in the face.
Step 1, Brick Breaker Create a Free Body Diagram
Step 2, Follow-Up Punch Find the net force (add up all your forces (using cosine
Step 3, See the Shadows: Find the Net force Fnet=<-Ft sin@, Ft cos@ - mg>
Step 4, Headbutt: Fnet= ma a=

Interlude, Break Period: Sin@=X/L

Step 5, Sweep the leg: Analayze Components y FtCos@ -mg = m*ay
Ft-mg=0
FT=mg
Step 6, Sweep the other leg: X:=-Fsin@=ma of x
Step 7, Wax on: Insert sin@ = X/L, -Ft x/l =MAX
Step 8, Wax off: Insert Ft=Mg
(-mgx)/L= MaX

Gather your thoughts: -Mg/L*x=Max
M's cancel out in the equation above ^.
-g/L x = ax

Step 9, Go for the crane kick: Look at the Force
-mg/L*x = max
Constant (k) = -MG/L
Linear Resting Force F=-Kxo
T=2π*Square Root of (M/K)
T= 2π*Square Root of (M/Mg/L)
T= 2π*Square Root of (L/G)

Homework is to do the hardest problem ever AND make sure you turn in Homework 4H. Next Scribe is whomever. Volunteer in class on Friday.... jk it's Sana.

great career advice from the creator of dilbert

Scott Adams, the creator of Dilbert, has a wonderful post on his blog with some great career advice.

Here's a quote:

If you want an average successful life, it doesn’t take much planning. Just stay out of trouble, go to school, and apply for jobs you might like. But if you want something extraordinary, you have two paths:

1. Become the best at one specific thing.

2. Become very good (top 25%) at two or more things.

The first strategy is difficult to the point of near impossibility. Few people will ever play in the NBA or make a platinum album. I don’t recommend anyone even try.

The second strategy is fairly easy. Everyone has at least a few areas in which they could be in the top 25% with some effort. In my case, I can draw better than most people, but I’m hardly an artist. And I’m not any funnier than the average standup comedian who never makes it big, but I’m funnier than most people. The magic is that few people can draw well and write jokes. It’s the combination of the two that makes what I do so rare. And when you add in my business background, suddenly I had a topic that few cartoonists could hope to understand without living it.

Suddenly, becoming extraodinary doesn't sound so hard.

2nd half of November 17, 2009

Today, for the second half of class, we discussed simple harmonic motion. This is produced by a linear restoring force. The restoring force is equal to the negative slope times the displacement or stretch. the velocity is never constant during simple harmonic motion and the velocity equals zero at the maximum displacement.

Then, we saw a weight hanging from a string move like a pendulum. We observed it moving back and forth and then in a circular direction. We timed the period of each. we then divided up into groups and found the length for one and the gravitational force for the other.

Tonight's homework is to finish 4H if you havent already or to work on the class lab. It was also recommended to read chapter 4. Mary Elizabeth can pick tomorrow's scribe.

Monday Scribe Post

So today we took a reassessment during class and got a sheet that had our overall reassessment grades. We talked about simple harmonic motion and watched a movie about it, where we saw the x and y components, but I never fully understood it. Simple harmonic motion has to do with spinning objects and squiggle graphs because that is what we saw in the movie. This is the type of motion that we saw::
http://en.wikipedia.org/wiki/File:Simple_harmonic_motion_animation.gif#filelinks
We also talked about the graphs that were for homework. C2 vs. C1 fully confused the class and I will try my best to explain the little bit that I understood. C2 is the constant/slope for the Air resistance vs. Terminal Velocity Squared graph and C1 is the constant/slope for the normal Air resistance vs. Terminal Velocity graph. So basically C2 is Fair/Vterm^2 and C1 is Fair/Vterm. C2 is a lot bigger than C1 when normal sized objects are involved, but with microscopic objects C1 is a lot bigger. That was monday.... and i dont really know who hasnt scribed but i dont think eliza has so... ELIZA!! :)

If you want to know more about drag forces

Wikipedia is a great place to start...

the physics of soccer balls

Now that you've learned about drag forces and projectile motion, you can put your skills to use and read about the trajectories of soccer balls. You'll probably find some of the notation in this article a bit overwhelming, but if you work slowly through it, and ask questions, you can get a lot from reading this article.

Trajectory Analysis of a Soccer Ball

Class on Friday Nov. 13th

The first thing we did in class on Friday was talk a little bit about projectile motion. Next we started discussing air resistance (also known as drag force). To demonstrate the effects of air resistance, Mr. Burk had a tube with air in it that contained both a feather and a penny. When he turned the tube upside down the penny fell downward much faster then the feather. Also the penny accelerated while the feather seemed to fall at constant velocity. In order to explain this we thought about the forces acting on the objects as well as the factors that affect air resistance. The only two forces acting on the objects are the gravitational force of the earth and the force of air resistance. The two factors that affect air resistance that we focused on were cross-sectional area and velocity. Since the penny weighs much more than the feather it has a much greater gravitational force. But the penny also has a significantly smaller cross-sectional area then the feather. Cross-sectional area is half of the normal area. We use cross-sectional area because air resistance does not act on the top of the objects. Since the feather falls at constant velocity it's air resistance must equal the gravitational force. When the force of air resistance and the gravitational force are equal it is called terminal velocity. This explains why the feather falls at constant velocity and why the penny falls with an acceleration of a little less than 9.8 m/s^2.

Next we talked about the physics of skydiving:

1. When a skydiver first jumps out of a plane his initial velocity is zero.

2. When he starts falling his velocity is about 10 m/s.

3. He keeps falling at an acceleration of 9.8 m/s^2 until he reaches a terminal velocity of about 200 mi/hr. His acceleration is 0.

4. When he opens his chute his acceleration becomes negative because the force of air resistance is greater than the force of gravity.

5. As his velocity decreases so does the force of air resistance acting on him.

6. As he nears the ground he reaches a new terminal velocity of about 5 mi/hr.

After that we went back to the tube. This time Mr. Burk used a vacuum to suck all of the air out of the tube. With no more air resistance when Mr. Burk turned the tube upside down the feather and the penny fell at the same rate. When he let the air back the feather shot up to the top of the tube because the air was traveling at roughly the speed of sound. Next we watched a video of a feather a hammer being dropped simultaneously on the moon. The feather and the hammer fell at the same rate but they fell very slowly because gravity on the moon is much smaller than on earth.

At the end of class we did a lab. We dropped coffee filters and used the motion sensor to track their terminal velocities. We started by dropping one coffee filter and then we did two, three etc. all the way to seven. We calculated air resistance by finding the mass of the filters and then finding the gravitational force. At terminal velocity air resistance is equal to the gravitational force. We did this lab to determine the effect of air resistance on velocity.

Hw was to graph f(drag) vs velocity as well as to linearize it.

I think Margaret wanted to be the scribe for Monday.

FAILCON: a conference dedicated to failing

It turns out that in the business world, just like the rest of like, of the of keys to great success is failing often and learning from one's mistakes. It can literally be worth billions. Good thing they now have a conference to teach you how...

Monday November 9th

In class today we went over the last question of 4G where the most important part of the problem was finding the x velocity component. Once this velocity was found, we could use the equation v=x/t. We knew the change in position was 56.6 m so we multiplied that by the velocity and got the time. We learned that a similar format could be used when finding the change in displacement with a gun fired at 45 degrees. The ladder part of class we worked in groups to write a good explanation to find the displacement at 45 degrees. The next scribe is Alexis

Reading graphs can get you on the national news

Remember Mr. Meyer? The math teacher who figured out that the express line isn't express at all? Well, he just got featured on Good Morning America.

A question: how do salad spinners work

You've probably seen a salad spinner before. Somehow, when it spins all the water leaves the lettuce. Washing machines do this too, and modern washing machines that spin in excess of 1000 RPM do an amazing job of getting almost all of the water out of your clothes before you even put them in the dryer.

Anyone care to take a stab at explaining how this works? You should try to explain this both from the inertia perspective (when you are outside the salad spinner/washer), and the non-inertial perspective (when you are inside the spinner, on a piece of lettuce, and subject to fictitious forces.

What is the best study break? Taking a walk in the woods

Scientists are interested in all sorts of questions, including "what is the best study break." Here's a study that tested how taking a short walk as a break from studying affected student's ability to memorize a series of numbers. It turns out that taking a walk in the woods significantly boosted student's memory compared to those who took a walk along city streets, or did not take a break at all.

What is the best way to take a study break?

Class on Tuesday

Class on Tuesday:

In class on tuesday we went over a lot of new things. First off my scanner hasn't been working, and I can't get an pictures of my notes up, so sorry about that. To go onm we went into a lot of detail about components and ended up figuring out that tan of theta = v^2 over gR. Then Mr. Burk had a turntable and set a ruler with three strings of the same length with a ball on the end. They were all identical except that each one went a little bit further from the center(radius of each one got longer). We had to predict what would hajppen when they rotated. We found out that the farther the ball was from the radius the closer to horizontal it got. Then Mr. Burk dropped a ball bearing and shot a ball bearing from a pinball machine like contraption and they hit the ground at the exact same time. This is because the horizontal velocity doesn't affect the vertical velocity. And since they both started with an initial horizontal velocity of 0 then they hit the ground at the same time. Then we proceeded to start watching/analyzing a mythbusters on whether if you drop a bullet and fire one from the same height, will they hit the ground after the same amount of time. We took many notes on this and with the data they gave us we could calculate really cool and complicated stuff.

The next scribe is Joe . . . he already made the post . . . I think Paxton is scribe for Friday.

The physics of free throw shooting

Now that basketball season is here, it's a good thing that physicists have worked out the best way to shoot a free throw.

See here: The physics of free throw shooting

Some tips from the article:

First, the engineers say that shooters should launch the shot with about three hertz of back spin. That translates to the ball making three complete backspinning revolutions before reaching the hoop. Back spin deadens the ball when it bounces off the rim or backboard, the engineers assert, giving the ball a better chance of settling through the net.
Where to aim? Tran and Silverberg say you should aim for the back of the rim, leaving close to 5 centimeters - about 2 inches - between the ball and the back of the rim. According to the simulations, aiming for the center of the basket decreases the probabilities of a successful shot by almost 3 percent.

The engineers say that the ball should be launched at 52 degrees to the horizontal. If you don’t have a protractor in your jersey, that means that the shot should, at the highest point in its arc to the basket, be less than 2 inches below the top of the backboard.
Free-throw shooters should also release the ball as high above the ground as possible, without adversely affecting the consistency of the shot; release the ball so it follows the imaginary line joining the player and the basket; and release the ball with a smooth body motion to get a consistent release speed.

“Our recommendations might make even the worst free-throw shooters - you know who you are, Shaquille O’Neal and Ben Wallace - break 60 percent from the free-throw line,” Silverberg says with tongue firmly in cheek. “A little bit of physics and a lot of practice can make everyone a better shooter from the free-throw line.”

Wedensday November 4, 2009

First Mr. Burk told us that we needed to be doing our self assessment and our reassessment that he gave us last week. Then he gave us our tests back with our corrections graded. Then we continued working on the lab where we analyzed the Mythbusters' efforts to determine whether a dropped bullet and a fired bullet would hit the ground simultaneously. They did, which makes sense, because vertical force, velocity or acceleration is independent from any horizontal force, velocity or acceleration. I couldn't find a video of this on the internet. We calculated the velocity of the bullets and the time it would take for them to fall to the ground, using velocity versus time graphs and the equations , and . Our homework is to do 4G and make sure that it is right, because Mr. Burk will grade for correctness. The next scribe is Paxton

if you have no data

This will help you...

Question About the graphs

Ok I get that we are supposed to make a Tension Force v Time graph but then how do we account for the other variables we changed like string length and mass size. because like we did 1 trial with 10g with tension force of 1.5 and string length 70 cm and got 3.74. However we did a trial with 1 g with tension force 1.5 and string length 30 cm and got 2.25. According to the graph those should be the same but they are not...?

can somebody please email me data from the lab on friday since I was not there.

thanks a lot, Dylan

Class: October 30, 2009

Today in class, we started off by breaking off into groups to write equations that expressed how to find centripetal acceleration or the factors that affect it. On the board, there was a triangle that represented an angle (theta), the hyptonuse (length of the rope the object was attached to), and the side opposite theta (the radius of a circle). There was also a free body diagram of Ft pointing northwest, a dotted line going straight up, an angle between those two lines represented by the same theta, and gravitational force pointing straight down.

The first question we had to answer was which way the net force would point: a little less than horizontally in the west direction.

Question 2 asked to draw a diagram of all of the forces acting on the object expressed in the free body diagram. Unfortunately, I do not know how to put my picture of it on the post so I cannot show it.

The next question was to find an expression for R by using the triangle. We knew that the sin of theta was equal to the R/L, so we also knew that R was equal to sin of theta multiplied by L.

Question 4 was to find an expression for the Fnet by using theta and Ft. We knew that sin theta would be equal to Fnet/ Ft if we looked at the free body diagram, so we also knew that sin theta multiplied by Ft was equal to Fnet.

Question 5: Write an expression for Fnet in terms of m and ac. We knew that f=ma, so we also knew that Fnet=mxac. We also knew that ac=4 times pi squared/ t squared, so Fnet=m times ((4 times pi squared)/t squared))

Question 6: Use the expressions from 3, 4, and 5 to make an xpression for Ft. Ft= Fnet/sin theta. Using the previous equations, we knew Ft=(m(4 times pi squared times R/time squared)/(R/L). Simplified, Ft=(m(4 times pi squared/time squared)/L.

After that we went and saw the halloween parade, came back, and did the lab. Our homework is to plot a force vs. acceleration graph of our results.

This is the 100th scribe post. The next scribe is Jason. Happy Halloween.

Brian Cox on Stephen Colbert

This is great. Stephen Colbert takes on the LHC, and then he interviews Brian Cox, rockstar physcist.

The Colbert Report	Mon - Thurs 11:30pm / 10:30c
Big Bang Theory
www.colbertnation.com
Colbert Report Full Episodes Political Humor Religion

The Colbert Report	Mon - Thurs 11:30pm / 10:30c
Brian Cox
www.colbertnation.com
Colbert Report Full Episodes Political Humor Religion

10/28/09 Class

We spent the majority of class time today going over HW 4F and the concepts covered by said homework assignment. Problem 1a involves drawing a free body diagram for a 40 kg chest sitting on a 20° ramp with a man pulling on a rope attached to the chest at a 30° angle. The question asks you to solve for the minimum tension force the man must exert on the chest to keep the chest from moving (this problem disregards friction) using a graphical method. First you should solve for the only force you know at first: the gravitational force. Using the equation

, you can calculate the downward gravitational force to be about 400 N by calculating . Once you draw this into your FBD, you should be able to see

another fact; both the normal force and the tension force have to act in set directions. The normal force acts perpendicular to the surface while the tension force acts at 30° to the surface. Because the chest is not accelerating (or moving for that matter), the net force must be zero and when the vectors are drawn tip-to-tail when you add them up, they should form a loop. Therefore, you can draw lines along the points where the vectors should pass through (for example, the tension force vector must pass through the tail of the gravitational force vector). Once you have done this, you can see the length's of the normal and tension force vectors. Now you simply need to measure the length of the tension force vector and use your scale to find the approximate magnitude of the force (it should turn out to be about 150 N). The following shows what your finished vector drawing should look like:

For problem 1b, you are supposed to solve the problem using the component method. The three sets of components are , , and (these could be derived by using sin, cos, tan trigonometry). Knowing that the net force is zero, you can add up all the x-components and all the y-components and both sums will be zero. Knowing this and after solving the equations for the tension force, the tension force turns out to be about 158 N (very close to the graphically found answer from 1a).

This is what we did in class today. Next scribe is Jason.

Google Doc

Everything on the google doc has either already been revised or someone has dibs on it. Should I revise something again?

Ares 1-X launches

Ares 1-X, the most powerful rocket ever built since the Saturn V (which was used in Apollo) was launched today. This is the rocket that should be the future of the space program, and will take us to the moon and possibly Mars.



This is a great video, and there's enough information here to figure out some pretty interesting things. For one, what is the average acceleration of this rocket in m/s^2? (FYI- Mach 1 = 340 m/s = speed of sound)

Class tues Oct 27

Today in class we continued to work on centrifical acceleration. While going over our homework, we first established our formula to find centrifical acceleration (V^2/R) We then went in depth a little more by finding a different way to do this. We used this other formula (4piR/T^2) It is very important to remember when using these formulas that this only calculates the magnitude of the acceleration (the direction is always perpendicular to the velocity) We then started to explore components and go in to more depth with Ac by looking a rocket powered six flags ride that looked really fun. From a simple youtube video, we were able to find tension force, the force of gravity, and the total net force as well as the radius. After a long day of note taking, Mr. Burk decided to be gracious by doing a fun demonstration of "blood" separating due to the high amount of gravitational force on a spinney thing, as well as let us watch a bunch of people experience high gravitational force on the spinney carnival ride. The science behind both of these demonstrations are that the high gravitational force is essentially pushing the substance against the surface causing them to "stick" Finally, Mr Burk gave us all a 5 minute demonstration of the lab that we will do tomorrow (while nearly tacking off my head). For some reason, my computer wont let me ut up my pictures of notes and/or the board.

How to Upload a Graph to Google Docs

go to here for the video

graph_to_doc

October 26, 2009

Today in class we spent most of our time trying to understand the centripetal acceleration using examples drawn on the board. The first example was of a roller coaster that does a loop. at the right side of the loop the acceleration is pointing south west, at the top it is pointed straight downwards, and at the left side it is pointed southeast.

After we looked at the centripetal motion of the roller coaster, we took the picture of a circle and took the velocity at four points on the circle. The first figure represents the velocity vectors of each point taken on the circle, and the second figure shows the acceleration of each of the vectors. The acceleration of vector 1 goes down to the left because when the components of normal force pushing to the left and gravitational force are combined, the result is a southwest pointing vector which is the acceleration.

After we finished looking over centripetal acceleration, we used variables to convert what we already know about centripetal acceleration into an equation to find acceleration. The final equation to find acceleration comes out to be V^2/R , where v is velocity of the object and R is the radius from the center of the circle to the object.

Hw: Re-do Hw 3e with the notes we took today

Next scribe is Dylan

I am really lost with problem two on homework 4E. I think that it will keep getting farther away but I don't really know what to do.

Homework 4E

What is the question asking in Question 2 of 4E?

Want to see scribes at other schools?

We aren't the only class in the world with a blog and scribes who post summaries of the day's class. Take a look at these, and you might find some good ideas:

Scribes at other classes

Centripetal Force?

I know I'll probably get it eventually, but i'm having trouble understanding what the centripetal force is. I kind of imagine the pennies in the mall but I don't really understand, everything from the equations, to the actual concept, or the diagram on 3e. Can someone help me out? First off how do you calculate the centripetal force and what is the difference between the centripetal force and acceleration?

class on Wednesday the 21st

Today we started off by getting back a boatload of stuff. We got HW 4E-4H, two reassessments, and a couple of packets. One of these packets was the FARMIPS packet. This is where we can write a problem and a solution that is a concept on paper and show it to Mr. Burk. If we do 40+ of these on 10 different concepts, we will get 5 extra points on our exam - that would raise your avg. by 1 point. Also doing this will raise your experience with doing these types of problems, therefore getting you an A on the exam. But this will take time, you can't just do it the night before the exam - so start now. Next, we took notes on the lab we did yesterday. These notes were discussing how to use trig to find that Fnet on the object is 0.

opp/hyp=Fn/Fg=sinO, adj/hyp=Fn/Fg=cosO, so Ff= FgsinO=mg*sinO & Fn=mg*cosO when O= the angle of the ramp. MU=mg*sinO/mg*cosO = tanOmax.

(There is a picture above of this lab.)

The last part of class was dedicated to Tug of War. We split up into groups and discussed how Adam or Bob could win the contest. We realized that whoever exerted more Ff on the ground would win, because the Ftension on the rope from both sides are equal due to N3. we tested this out by putting 4 people, shoeless, one one side while the other 4 had shoes. With socks on, Ff is much less than with shoes on, so the shoe side owned because they exerted more Ff. Then later Jason almost got his shoulders dislocated. Homework is 4E and to give 30 mins. to the paper.

NExt scribe is Burge-asaUR.

Getting it wrong: surprising tips on how to learn

There's a GREAT article in scientific america talking about some of the latest research on how to learn.

When you have 15 free minutes you should ready this. (You probably have 15 minutes when driving to school, so why not download instapaper to your iphone, and read it on your phone).

Some highlights:

People remember things better, longer, if they are given very challenging tests on the material, tests at which they are bound to fail. In a series of experiments, they showed that if students make an unsuccessful attempt to retrieve information before receiving an answer, they remember the information better than in a control condition in which they simply study the information. Trying and failing to retrieve the answer is actually helpful to learning. It’s an idea that has obvious applications for education, but could be useful for anyone who is trying to learn new material of any kind.

By challenging ourselves to retrieve or generate answers we can improve our recall. Keep that in mind next time you turn to Google for an answer, and give yourself a little more time to come up with the answer on your own.

The article seems like it practically lifted my FARMIPS idea from today's class, but it talks about how you can adapt this method to any course—imagine making a super study guide for history, or English. How much could you rock those classes?

Google Docs

I don't know how to put my graphs up onto there either! If anyone would like to help or if anyone wants to tell me how to upload it that'd be great.

October 20th

Today we started off a reassessment. I'm not sure if I'm allowed to talk about it.....

Anyways, then we talked more about graphical vector constructions. Our goal was to be able to construct an acceleration vector at any point on the graph. The first thing we did was find the scale. Then, we found the change in position from one point to the next, and divided that by the change in time to get the change in velocity for that vector. Then, we repeated that with the next two points to find that velocity. We used those two velocities to find the acceleration at the point in the middle of the 3 points we used. To find the average velocity, we made a point in the middle of the first and second points given and drew a vector through the second point that was as long as the velocity we found earlier. We did the same for the next 2 points. Then, we connected the two vectors and made a resultant vector. This resultant vector is the velocity it takes to turn in a different direction and is also the direction of the acceleration. This kind of change in velocity is called centripetal. When the only thing that changes in velocity is speed it's called tangential. In the second period of today's double physics we did a lab that had to do with ramps and frictional force on blocks. We set the ramp at a 15 degree angle and calculated the frictional force by making a graphical vector.

That's all we did today during physics. Tomorrow's scribe is Gaston!

Paper

Hey I thought I had dibs on how mass affects friction (cough cough Gaston cough), but now that it's already written I can't really find anything more to write in the document.. Everything that was needed to be done was written already.... what do I do?

google docs issue

Google docs wasn't letting me copy and paste my graphs so I had to make a table... I am posting my graphs on the blog so anyone who would like to try to post my graphs can. Also, I only made one table because I have been attempting to paste my graphs for a very long time.

by the way if you miraculously can put my graphs up, you can just delete my table.

4d number 4

hey guys,

on question number 4 i am struggling on figuring it out... how is it possible to find the period without knowing anytimes or any other forces?

This could be you in 3 years

Want to see what other students, just like you can do if they put their minds to discovering something new in science, and work at it for 3 years?



Watch this. Oh, and if you were to win one of these awards, your worries about getting into a good college would be over. Colleges (all of them) would actively recruit YOU to come to their campus.

Here's the link to the description of this year's winners.

Why you should think about doing summer research in science

So you guys are through your first 9 weeks of physics, and now you have a better idea for why I showed you this picture on day 1.



Yes, this class is hard (but it should NOT feel painful, let me know if it does). Just like a great workout, you should have a sense of real accomplishment from this class. You should also know as your teacher, I'm often just like that spotter, pretty amazed that you're lifting all the weight you're lifting.

But my point is that now that you're getting a good workout, you should put your muscles to use. After all, lifting weights in the gym is fine and all, but the real fun is being bigger, faster or stronger in the sport you love.

In the world of science, science classes are the workouts (practice) and doing real research are the games. Believe it or not, you're ready to join a lab and do some real research starting tomorrow, and certainly by this summer, you could be part of a group of researchers who are doing cutting edge work on all sorts of amazing things.

Unlocking the secrets of the universe (especially when no one has discovered them before) can be immensely rewarding. Fame fortune and lots of prizes await you. But the most rewarding thing really is the fun you have from working in a lab with lots of cool people, playing with crazy toys, and discovering something no one has ever discovered before.

If you're interested in learning more about this, the time to start thinking about it is now. See me.

ps. Do click on the links above, they go to some cool stuff.

Paper

Hey everyone, can I claim the part about how mass affects the friction? Thanks! Oh, and I requested permission to edit the post but it's really late.... I don't know if it'll be accepted in time...

Hey guys. So I tried to get to the google doc. I logged in and everything, but I can't figure out how to edit it. And I started way too late...

paper

Hi guys. Can I get dibs on surface area? That it the topic I understand best.

Thanks, Dylan

Success requires hard work (but not all in one day)

This is a nice blog post that elaborates on many of the themes we've talked about before.

Success Requires Hard Work (But Not All in One Day)


Why not start writing a book?

While success may require a lot of hard work, that doesn’t necessarily mean that work is hard to do. A book may contain 80,000 words of carefully edited content, that’s a lot of hard work. But writing 800 words almost every day for four months isn’t hard to do.

Link to our paper

Here's the link to our paper

Factors that affect the frictional force on a sliding block.

October 19

Today in class we looked at a picture of an accelerometer and discussed the uses for it. I thought it was really interesting that they are used in the iphone to rotate the screen.
Then, we talked about the lab report that we are doing as a class. Tonight, everyone will write an entry that will help us come closer to finishing this project. We are including and introduction, apparatus, information about how mass, surface type, surface area, and velocity affect the blocks, modern studies, and a conclusion.

We went over our homework 4C. It involved adding and subtracting vectors.

For the last few minutes of class, we started graphical vector constructions. We found the change in position and the velocity from one point to the next. It is a better approximation if you find the change in position and velocity between the two points.

Homework for tonight is to write an entry for the lab report and homework 4D if you have time.
tomorrow's scribe is...Mary Elizabeth :)

If you liked the video on gravity...

You should check out the entire program called The Elegant Universe. You can watch all three hours online for free. It provides an explanation for string theory, which is a possible explanation for all the particles and forces in the universe, all being made up of tiny strings that exist in 10 dimensions. -

The website for the program is equally fantastic.

10/16/09

We started off class today by reviewing the concept of the two rooms. There are two sets of rooms, the first of which has one room in the middle of deep space and the other falling with the acceleration of g, or approximately 9.8 m/s^2. From the inside of these two rooms, there isn't an experiment that can be performed to distinguish the two. For example, if you release a ball in the air in either elevator, it will appear to stay in one place. In the deep space room, this is because it is truly weightless. For the falling room, this occurs because the ball accelerates downward at the same rate as the room and so appears to not move in relation to the room and everything in the room. The other set of rooms has one sitting on the surface of the Earth and the other in a deep-space rocket with an acceleration of 9.8 m/s^2. Einstein believed that these two rooms should be indistinguishable from the inside as well (for example, a ball dropped in the room on the Earth will accelerate downward at 9.8 m/s^2. The ball in the rocket room would attempt to keep a constant velocity due to its inertia but would appear to accelerate downward because the room is accelerating constantly so the floor is actually striking the ball. The ball drops on the surface of the Earth due to its gravitational mass while the ball in the rocket appears to fall due to its inertial mass). However, if he was to go by this theory, then light would need to behave the same in both rooms as well. A laser shined in the rocket room would attempt to move in a straight line, but since the room is accelerating constantly, it actually strikes a point on the wall slightly below where it would strike if the room had a constant velocity. Therefore, the laser would need to behave the same on the surface of the Earth, bending below a completly straight path. Because of this, Einstein believed that gravity must have some affect on light, a new idea for his time.

On a similar note, we also discussed the basics of Einstein's theory of general relativity. Before Einstein's time, Newton's theories regarding gravity were widely accepted; Newton stated that the force that makes things fall and the force that keeps things in orbit were one and the same, the force we know as gravity. However, not understanding how gravity worked, he more or less saw gravity as a mysterious force that large objects used to grab smaller objects (i.e. the Sun grabs the Earth and keeps it in orbit). However, Einstein proposed a new theory in the early 1900s and found a way to understand gravity. He thought of the first four dimensions as a single plane of "space-time fabric." Large, heavy objects, such as planets or stars would create dips in this space-time fabric which would alter the paths of things moving through the dip. Therefore, the force associated with gravity is really caused by objects being influenced by dips in the space-fabric. The following picture shows the Sun bending the space-time fabric and how this affects the surrounding planets:

As you can see in this picture, dips in the space-time fabric can not only change the paths of planets, but it can also influence the path of light. Today, this phenomenom is seen when we are able to observe stars that should be physically blocked by a large object, say the Sun. The following picture shows the light from a star bending around the Sun:

Point A in this picture is the actual position of the star. But because light bends around the Sun, we perceive the position of the star to be Point B, which would be the actual position of the star if the light was traveling in a straight line.

Finally, we also talked about frictional forces. Unlike normal forces which act perpendicular to a surface, frictional forces act parallel. However, these two kinds of forces are strongly related; the size of the frictional force depends on the size of the normal force (i.e. the harder you press two surfaces together, the greater the amount of frictional force). The general term "friction" can be divided into two different types of said force: static friction and kinetic friction. Static friction occurs when two surfaces have no relative motion, for example if a block is on a slanted surface but doesn't move. When surfaces have relative motion, kinetic friction occurs. You can see this when you slide a block along a tabletop. Friction is often quantified by using something called the "coefficient of friction." This is defined as the frictional force between two surfaces at any given moment divided by the normal force at that moment. The higher this number, the more frictional force for a smaller normal force (i.e. a big frictional force). After the friction talk, we split into groups and performed experiments to find the factors that affect or don't affect frictional force (we tested factors like mass, normal force, surface area, velocity, etc.).

These are the things we did in class today. Next scribe is Eliza.

what is this?

Propsicle to the first person to figure it out...

What's it like to win the nobel prize?

Carol Greider, winner of the 2009 Nobel prize for discovering discovering telomeres bits of seemingly useless DNA on the end of each of your chromosomes that progressively get shorter as you age and your cells reproduce. As it turns out, these bits of DNA are deeply linked to the aging process.

Anay, Dr. Greider has a fantastic interview with the NYT in today's paper, and one quote is absolutely worth reading and pondering.

Q. DID YOU ALWAYS WANT TO BE A BIOLOGIST?

A. My parents were scientists. But I wasn’t the sort of child who did science fairs. One of the things I was thinking about today is that as a kid I had dyslexia. I had a lot of trouble in school and was put into remedial classes. I thought that I was stupid.

I hope you'll take away the knowledge that if you struggle in science, or any subject, it is no measure of your ability to succeed in that field or your intelligence. Truly, hard work and persistence are the key to success at any level—even winning a Nobel prize.

Wenesday October 7

Today we started to work on the gravitational force lab. The lab is mostly about the gravitational force vector which on earth is 9.8N/kg.

class on 10-09-09! part 2

class on 10-09-09!

On Friday, we had a double period. It started off with getting the Reassessment 4 back. I guess i shouldn't talk about it, don't know if anyone still hasn't taken it. The Hw FOR friday was to finish the springs/Fg lab. It should be finished but we didn't go over it.

Instead, we started taking notes on the elastic force packet. We started by talking about how Hooke's law applies to our elastic force/spring stretch graph. The reason the line doesn't go through the origin is because when elastic force=0, the stretch of the spring is about 7 cm. Hooke's Law is that "Fs(change of x)=-k * (change of x)." The change of x is the stretch of the spring and k is the constant of proportionality. It's negative because change of x is opposite the Fs. Hooke's law is an empirical law because it is done by experiment, but it only works for us until the spring is stretched a certain distance, then the constant of proportionality changes.

Next, we talked about the FBDs of an upper book on a lower book. We put the forces in order of greatest to least to compare. Then we realized that force 1=force2=force3. This is because 1=3 (action/reaction - N2) and 1=2 (a=0,Fnet=o, Fg=-Fn - N3).

Then, we did an experiment with a mirror reflecting a laser beam. We put a heavy object on the table to see if the atoms in the table would compress and the light of the laser would rise. This actually did happen because the atoms of the table were compressed and became closer together because of the force exerted on it. With this, the bonds on the atoms pushed back even harder because of the reaction force.

Lastly, we took some notes and did a lab on Fg and Fn of a 700 N man standing on a scale in an elevator. In the notes, we said that when an elevator has a constant v, the scale will read 700 N. But when the elevator accelerates upward, the bottom of the elevator pushes on the man and he pushes back. So the reading > 700 N. But when the elevator is accelerating downward, the Fn on the man decreases. So the reading < 700 N. We put this into a real test when we all crammed into an elevator and saw Alexis's Fn increase and decrease as we did the respective tests.That's all on the day. HW: Web Assign Week Evaluation 8, homework 4B, and read Chapter 4:1-2. NEXT SCRIBE: it's Matthew, unless you've gone twice.

Question re: HW 4A

I do not understand 5c) and d) on homework 4A. For a) I got 2.4m therefore for b) I got 1.2m/s but then how do you find the instantaneous velocity when there is nothing past or before?

The nobel prize in physics

The Nobel prize in physics was just awarded today for the fundamental breakthroughs that led to two things you use just about every day. Fiber optics, the technology that allows light to carry gigabytes of information through optical fibers, allowing you to stream entire movies on your computer, or make a phone call to the other side of the world for pennies.

The other breakthrough was the development of the CCD, the charge coupled device, which you'll find in any camera phone, or digital camera. This discovery allowed us to convert tiny packets of light into electrical signals, which heralded digital photography. Once we started putting CCDs into telescopes like the Hubble, we could see incredibly feint objects billions of light years away, allowing us to peer at the universe as it existed billions of years ago.

NYT story on the physics nobel prizes


A great description of the discoveries from the Nobel Prize Committee

Tuesday October 6th Physics Class

In class today we started off by getting a few handouts. We got the chapter 4 reading, HW 4a, HW 4b, and a packet for the lab.

Next we expanded our knowledge of vectors. To subtract a vector A from a vector B, add the opposite of vector B. The opposite of a vector is just the same vector going in the opposite direction. You can also subtract vectors by putting them tail to tail.

http://mathforum.org/~klotz/Vectors/subtraction.html

We also found that to find -(vector A + vector B) you add the two vectors and take the opposite of the resultant.

After our discussion of vectors we started a new lab. Our first task was to find out how many Newtons are in one Spring Unit. After we did that we stretched an uncalibrated spring different amounts, measured the force, and graphed force vs. stretch of the spring (∆x). This lab is to be continued.

At the end of class we turned in the vector lab. Homework is 4a.

How do you make dry ice?

A number of you have asked questions about how to make dry ice. Ask the internet, and it delivers:

Monday

Today we took our assessment! I cannot talk about the assessment because some people haven't taken it yet. We also got back an overall concept sheet with our assessment grades and a sheet that will guide us through getting our averages. I was going to find a cool video about physics to put on the blog but I spent 30 minutes on youtube and I could only find this....

Our homework is the vector lab!

The next scribe is..... Sana!

http://www.youtube.com/watch?v=Y8skDy9Nn9I

I don't understand....

Hey everybodyy..

There are some things from the Unit 3 Major Concepts list that I don't quite understand and I'd like for you to help me out by explaining them?

3.4.4

Can you interpret graphs of acceleration vs force and acceleration vs 1/mass to find additional.... (it stops there)

3.5.1

Do you understand how the constant of proportionality, k, in N2 is determined by the units we.... (it stops there again)

3.6.1

Do you understand how to measure inertial mass?

3.7.2

Can you apply N3 to resolve the horse/cart paradox?

Thanks soo much!!

10/2/09 Class

The first thing we did in class on Friday, was to get back our 3E and 3F homework. We then talked about how the earth has a huge mass, which means it has a huge inertia. The moon and sun can change the velocity of the earth, it's always changing because we're orbiting. We exert force on the earth, because the earth exerts a gravitational force on us, but the force we exert is not enough to change the velocity of the earth. Footprints are proof that we put force on the ground. THe normal force of us on the earth equals the gravitational force of us on the earth, but if we are in quicksand there would be less normal force.
We went over many of the homework problems. The solutions are on the blog. Just dropped, a heavy dart and a light dart have the same acceleration. a=fnet/m, and if the darts were shot by a gun, the mass would be larger for the heavy dart. So it would have a larger acceleration. This happens because by the time the dart has left the gun, it already has a larger velocity.
When two vectors are added, the sum can be anything from zero to the sum of the lengths of the vectors. If you're confused about how to arranget the vectors, ask yourself "Is this something I could walk?"
The vector activity is due Tuesday. The vector activity sheet shows us how to do vectors on the calcuatlor, but be comfortable doing this with a ruler and protactor before you use the calculator. Our test is tomorrow. Study. Don't forget about the Unit 3 Review Sheet for practice.
The next scribe is Margaret

Want to know more about dark energy and dark matter? Check out this video.

Patricia Burchart, a particle physicist and professor at Stanford explains all we know about Dark Matter and Dark Energy. This is a great talk, in 16 minutes, it will explain our latest understandings about what our universe is made of.

September 30th Physics Class

Today we first turned in Homework 3F. At this point both 3E AND 3F should be turned into Mr. Burk. Then as class began, we reviewed vectors and scalars.
Some Examples of Vectors:

• Velocity
• Speed
• Acceleration
• Force
• Etc (Forces with Direction)
  

Some Examples of Scalars

• Quantities
• Time
• Position
• Temperature
• Etc (Forces without Direction)

Then we talked about how the earth is a giant magnet with a north and south pole just like a small magnet has a positive and negative end, and how a compass ( a magnet used for telling direction ) exerts a force on the earth but does not affect the earth greatly because it has a small mass. However the mass of the earth causes the magnet to spin around in the direction of north.

Then we finally proceeded to the last section of the Vector's lab, which involved going to the orange circle across from Campbell Hall, then we followed different bearings using the compass. Also as we followed the direction we timed the time it took to get there. We also measured how many meters one of our regular strides was. We then divided the number of meters per bearing by the number meters per stride to get the number of strides we needed to walk for each bearing.
They were as follows:
75m 30 degrees South of East
Go Down to the Path in front of the staircase infront of the bookstore.
50 m 35 degrees North of East
Down to the stairs infront of the Campbell Hall Parking Lot.
90 m 30 degrees North of West
Down across the Campbell Parking Lot to the path to PAWS seal.
50 m 50 degrees West of South
Down the pathway to the PAWS seal
75 m 30 degrees North of West
At this point using your compass you should be in front of Turner.
125 m 6 degrees West of South
Walk across down the path to the Turner carpool lane.
120 m 34 degrees North of East
Walk across Broyles Field to the Sculpture.
And that concludes the physics class. Next scribe is Mary Elizabeth.

Monday September 28

We started out today in class going over vector addition. We discussed how vectors represent two quantities, force (or velocity, acceleration, or displacement) and direction. Then we continued working on our vector packet. We sketched and then added the vectors of two spring units pulling a block as illustrated below.

This is the arrangement of the block and the springs. The springs are the gray lines.

This is an illustration of using the tail to tip method of adding vectors. The two gray lines represent the springs and the blue line represents the actual force exerted on the object.

Then, we took a washer and three spring scales and pulled on the washer with all three spring scales so that it wasn't moving. Then, using a giant circle with degree measurements on it and the reading on the spring scales, we found the force and direction that each of the spring scales applied to the washer. We graphed and then added these as vectors, which should have looked something like this.

Our Homework was worksheet 3F, which had 2 pages. The next scribe is Rahul.

useful tutorial on vector addition

If you're a bit unsure about what we did today with adding the three forces on the washer, you might want to take five minutes to follow along with this quick step-by-step tutorial.

Adding vectors graphically

You can find many more tutorials by googling "graphical vector addition", and even some interactive demos by googling "graphical vector addition applet."

Newton and Newton's 3rd Law

Here's a fascinating letter from The Physics Teacher (A very cool magazine, if I do say so myself), about Newton's own discovery of the idea of forces coming in equal and opposite pairs. I've bolded the most important part

NEWTON AND NEWTON’S THIRD LAW
Just as students have difficulty with Newton’s third law as discussed in the article by Lehavi and Galili, it is of interest to realize that Newton’s under- standing of the significance of the mutual interaction of bodies in their motion did not occur until very late leading up to his writing of the Principia. Cohen published an article on this, which also appeared as an appendix in a revised and updated version of his book.

Newton wrote an essay entitled “De motu” in which he described a calculation of the orbit of a planet in our solar system. He ran into the problem that his calculation did not fit the actual data sufficiently. He realized that assuming a stationary Sun was a potential source of error. He recalculated, but this time he allowed the Sun to move in response to the pull of the planet. The revised calculation yielded numbers within the error of measurements of the orbits of the planet available at the time. Apparently, the notion of the third law of motion was not an explicit and automatic part of Newton’s thinking until this point.

According to Cohen this work was completed shortly before Halley’s visit with Newton, which led to the writing and publication of the Principia. This is in distinct contrast to the impression one often gets from descriptions of Newton’s life in physics textbooks that he went home to avoid the plague dur- ing college and in two years worked out all of his contributions to physics. We should know better and do better in our textbooks because serious historical scholarship on Newton is now eas- ily accessible.

The final paragraph in the article by Lehavi and Galili illustrates the magnitude of the problem caused in physics education by the emphasis in texts on presenting as much of the canon of physics as possible. At best students develop a kind of technician’s view of physics, which is that the goal of learn- ing physics is to remember a list of calculations and facts. In doing so students miss the essence of physics, which is the construction of4 explanations of physical phenomena. Is it any wonder then that students yearning for such intellectual challenge choose other fields to go into?

Dewey Dykstra
Boise State University

Friday, September 25

Today in class Mr. Burk gave us back our Homework 3d. We then went into a long discussion about the Inertial Balance vs. Regular Mass Balance. The inertial balance is what is used in space to measure weight, because everything is moving in a constant free fall, so there is not enough gravity to be able to measure. In the end the measures of each kind of mass end up being the same.

After we discussed the two types of balances, everyone went to the lab table and we discussed the free body diagram of a horse pulling the wagon. "According to the horse", he should not be able to move the wagon because every force he puts on the wagon, the wagon counteracts equally and oppositely. After much discussion, we came to the conclusion that the friction of the horse pushing against the ground gives the horse the extra leverage to actually move the wagon.

The final activity we did in class was to begin the vector lab. Mr. Burk had a contraption of two rulers screwdrived together so that one ruler went out 50 cm or 1 spring unit before the other ruler crossed it perpendicularly. First we did a control test of 1 spring unit, and then wrote predictions for the two spring units. Most everyone said it would be exactly double even though the springs go out at angles and are not pulling straight in front of the cart. It ended up that the two spring units on the ruler contraption only pulled the cart with an acceleration 0.7 m/s/s faster than one spring unit, which was not close to double. We then tried to figure this out, and did not finish the discussion, but so far it looks as though it involves finding the leg of the 45 45 90 triangle and doubling it to find the amount of force.

Homework: Finish the Inertial Balance lab and Homework 3E

Next scribe is Paxton.

On the subject of bottled water

Hi All,
on friday we had a semi-serious discussion about the evils of bottled water. Here's a link to the article I mentioned discussing some of the problems and environmental harms of the bottled water industry.

Message in a bottle

Some crazy facts:

• Americans spent more money last year on bottled water than on ipods or movie tickets: $15 Billion.
  
• We pitch into landfills 38 billion water bottles a year -- in excess of $1 billion worth of plastic.
  
• We're moving 1 billion bottles of water around a week in ships, trains, and trucks in the United States alone. That's a weekly convoy equivalent to 37,800 18-wheelers delivering water. (Water weighs 81/3 pounds a gallon. It's so heavy you can't fill an 18-wheeler with bottled water--you have to leave empty space.)
  
• And in Fiji, a state-of-the-art factory spins out more than a million bottles a day of the hippest bottled water on the U.S. market today, while more than half the people in Fiji do not have safe, reliable drinking water.
  
• If the water we use at home cost what even cheap bottled water costs, our monthly water bills would run $9,000.
  
• Half the wholesale cost of Fiji Water is transportation--which is to say, it costs as much to ship Fiji Water across the oceans and truck it to warehouses in the United States than it does to extract the water and bottle it.
  
• Sometime this year, Fiji Water will eclipse sugarcane as the number-one export from Fiji. That is, the amount of sugar harvested and processed for export by some 40,000 seasonal sugar workers will equal in dollar value the amount of water bottled and shipped by 200 water bottlers.
  
• Worldwide, 1 billion people have no reliable source of drinking water; 3,000 children a day die from diseases caught from tainted water.
  

Anyway, if you read this and still think "bottled water tastes better" let me know, and I'll be happy to set up a test to show you that you can't distinguish bottled water from the water right out of the tap in Westminster, or your house for that matter.

Difficulty with the Lab

Hey, I'm not sure if anyone else is experiencing this problem but with Part 3 of our lab I really cannot come up with a way of finding the mass of the clamp. I know we did something with 6 clamps and 200 grams and I have data for that but I do not think my formulas are correct. Can anyone help me?