You CAN change the world

Never doubt that a small group of thoughtful, committed, citizens can change the world. Indeed, it is the only thing that ever has.

--Margaret Mead

Boy, 7, raises $240,000 for Haitian Relief.

Tonight's (1/25/10) Homework

Hey guys, I was having a little bit of trouble with 2c (see how Kinetic Energy vs. Distance Fallen graph and Gravitational Force vs. Distance Fallen graph help to define Gravitational Potential Energy). I feel like Gravitational Force and Gravitational Potential Energy are kind of the same thing... I'm kind of confused about the difference between the two/the 2c question in general if you couldn't tell already. Anything would help, please comment! Thanks so much!

Hard problem 3

Hard problem 2 is dead——if you helped solve it, be sure to claim your propsicle.

Hard problem 3 can be found here.

An important point about 5C

A very important point came up today when a few students were discussing 5c. The question was which of the following two graphs is the right answer. It turns out the bottom graph is right. Why?

Hard problem, still not quite solved...

It's begging for you to finish it off... Have mercy...

Hard problem

Big Ideas from 1/20

We discovered big understandings from force vs. displacement graphs and energy vs. position graphs. The area in a force vs. displacement graph is work. The work done by the spring force is - 1/2(k) (change in x)^2.
Energy depends on displacement, and a large displacement leads to a large energy. A small displacement leads to a small energy. For the kinetic energy vs. displacement graph, the total energy was constant. The difference between the total energy and the kinetic energy is the potential gravitational energy.

Class on Friday Jan. 15th

In class on Friday we talked about how to go about solving energy problems. Mr. Burk gave us some steps:

Guidelines For Energy Problems

1) Start by defining a system

2) Give symbols meaning (ex: instead of looking at a symbol like K and thinking of it as just K, think of it as change in kinetic energy)

3) Do everything symbolically

Also in class, we talked about power.

Also,

Power is measured in Joules per second or Watts. 1 Joule per second=1 Watt

Homwork is to finish 5C

Monday's scribe is... Jason

Today in class...

Today, we started class by discussing how a single point particle can be thought of as a piggybank. and money as a whole is considered energy. i thought that was a cool analogy!!

Energy is put into an object, but then it must leave the object at some point. if more energy is put into an object than the amount that leaves, the object is gaining energy. if more leaves an object, it is losing energy.

Then, we looked at our graphs. K should be between 400N/m and 800N/m. The force of the spring is opposite the stretch. Just as a review: work equals force times change in displacement. (W=F*change x)

Homework is to finish 5b and start 5c. tomorrow's scribe is Sana!!

Blog Post 1/12

First off I would like to take the opportunity to thank Dylan for his choosing me, as I am really excited about talking about today's Big Idea...

That aside, Today's Big Idea is talking about the change in Energy being the same as Work done by the Surroundings and other factors (to be determined later). First off we discussed the SPP, or Single Point Particle which essentially labels one object in a system as a single point. Some things to remember about the Single Point Particle. First off, Single Point Particles only have K or Kinetic Energy. A good way to think about a Single Point Particle is like a rock. The surroundings (The Earth) does work on the Rock (Makes it fall). Therefore energy is transferred from the Earth to the Rock. Positive work for the Rock and Negative Work for the Earth.
Also we discussed the next sort of system separate from the Single Point Particle System. We can call this a multi part system. Basically this type of system includes multiple objects. To take our rock example further we can say that the rock includes both the Rock and the Earth. This way we can more effectively observe the LoCoE (Law of Conservation of Energy: energy is neither created nor destroyed, it simply changes forms). The energy although moving inside the system does not change overall for the system in relation to outside surroundings to the system. This is key in remembering that all energy is transferred between systems.

Those are the two basic big ideas. If anyone has any specific questions they can just post a comment below and I think I'll be able to answer them. Next scribe is Eliza.

class today

Class today.
Short and sweet

Big Idea: Today we looked at the different types of energy relating to gravity and weather they are positive or negative depending on the scenario. We also talked about weather or not our system should include one point or multiple, and how this effects the system and the energy we need to look at.

tomorrow, Rahul is the blogger

SAT II practice questions

Here's a link to some SAT II practice questions from the college board.

SAT II practice questions

You should see a number of questions are quite easy and quickly answerable:
In particular #5, 6, 12, 21, 22, and 23 are all easily within your grasp.

With a little effort, you should be able to use what we're doing now to do problem 11 and 15.

Most of the rest, will be covered throughout the year, with the exception of the problems on optics, which we probably won't get to—-this is why you need a book to study from.

Here are some other resources:

Sparknotes SAT II physics


SAT II Wikibook--not that helpful

Cracking the SAT II: one of the better SAT II review books, but none of them are great. All you really need are lots of problems.

As always, I'm happy to help you dominate the SAT II, but it's up to you to create the plan that will lead to success.

homework for tuesday

Be sure in addition to 5A that you also read and answer some of the questions from your classmates:

5.1 and 5.2 Questions

Burj Dubai Base Jump

Two basejumpers just set the world record for BASE jumping from the world's tallest building the Burj Khalifa (formerly called the Burj Dubai), from a height of 828 m.

Check out the video below:


Two questions:
1. Why didn't this video take the 13 seconds you calculated take an object to fall to the ground?
2. What was the average velocity of the skydiver? How does this compare to the velocity an object falling only under the influence of gravity would have when it hit the ground?

Hard problem 2

Someone tore through the last hard problem very quickly (I added a bit to the end). This is incredible work. Whoever did this should certainly count it as a FARMIP, and anyone else should try to do it themselves as a FARMIP.

Here's another problem.

Good luck.

your questions from the reading

Hi Guys,
I hope you're enjoying a relaxing snow day. I've put all your questions together into a wiki page below. I think it would be a good exercise for us to try to answer these questions together as a class.

In order to edit the questions, you'll need to create a free account with pbworks.

5-1 and 5-2 Questions

If you can take a moment or two to read over these questions, and if you have some ideas, offer an answer or two, that would be terrific.

Also, if you haven't sent me your questions yet, please do so.

Class on 1/6/10

The big idea from class today was the big idea of energy, it is neither created nor destroyed in a given system but it only changes form. We demonstrated this through the analysis of Net force, change in position, mass, and change in velocity. After simplifying the equation, we found if kinetic energy goes up, interaction goes down, which shows the change in energy but none is lost.

Next scribe is Dylan

the physics of snow

Since it's on all our minds....

Why does snow make everything seem much quieter?

Can it get too cool to snow?


Designer snowflakes from the lab

Physics of snowbaording (don't expect to do much of this tomorrow).

Another hard problem

Here's an idea if you're looking for something fun and challenging. I've posted a hard problem to google docs:

Hard problem for fun and challenge.


Give it a shot. It's a google doc, so you can just go and write questions, or try to sketch a FBD.

Study Hacks talks about deliberate practice

Another awesome blog post on why just working at something doesn't always make you better. You have to practice in a deliberate way.

What a study of chess experts teaches us about building a remarkable life

Some highlights:

What is deliberate practice?

It’s designed to improve performance. “The essence of deliberate practice is continually stretching an individual just beyond his or her current abilities. That may sound obvious, but most of us don’t do it in the activities we think of as practice.”

It’s repeated a lot. “High repetition is the most important difference between deliberate practice of a task and performing the task for real, when it counts.”

Feedback on results is continuously available. “You may think that your rehearsal of a job interview was flawless, but your opinion isn’t what counts.”

It’s highly demanding mentally. “Deliberate practice is above all an effort of focus and concentration. That is what makes it ‘deliberate,’ as distinct from the mindless playing of scales or hitting of tennis balls that most people engage in.”

It’s hard. “Doing things we know how to do well is enjoyable, and that’s exactly the opposite of what deliberate practice demands.”

It requires (good) goals. “The best performers set goals that are not about the outcome but rather about the process of reaching the outcome.”

Now here's the kicker—since deliberate practice is so hard,

Unless you’re a professional athlete or musician, your peers are likely spending zero hours on DP. Instead, they’re putting in their time, trying to accomplish the tasks handed to them in a competent and efficient fashion. Perhaps if they’re ambitious, they’ll try to come in earlier and leave later in a bid to outwork their peers.

But as with the intermediate-level chess players, this elbow-grease method can only get you so far.

That's right—most students, athletes, aren't doing anything close to deliberate practice.

What do you think will happen when you start doing deliberate practice?

A puzzle

In the interest of improving the blog, here is a puzzle that I found in the New York Times. Some of the questions it poses are relevant while others require more background knowledge than we have. A word of caution: it uses Tom Cruise and Nicole Kidman as examples. All the same, here it is.

When Tom and Nicole were in love, they apparently exchanged a pair of Oscar-type statuettes of each other made of solid gold. After their break-up, these former symbols of love became symbols of pain. To ease the pain, Tom Cruise hit on a stategy of “placating density.” Sorry, that should read “placating destiny.” You have to take an object that you associate with the loved one, and submerge it in the middle of a lake. If the water level rises, it symbolizes that your mental tide has turned, and it helps you to move on.

1. So, as shown in the figure, Tom Cruise took the solid gold statue of Nicole Kidman, rowed to the middle of a lake, and tossed it overboard. Did the water level rise, fall, or stay the same when the statue sank to the bottom, relative to the level when the statue was in the boat? Why?

1. a) What’s wrong with the path of the tossed statue in the figure?

1. b) It turns out that in his haste, Tom Cruise ignored another cardinal tenet of the metaphorical remedy. It seems that to get the full mental benefits, you cannot toss the pain-associated object. You have to release it gently with your hand still in contact with it when it touches the water. Can you think of a way that Cruise could have done this so that the water level rose when he released the statue in the middle of the lake and it sank to the bottom? (Note: The lake is too large for him to stand at the shore and drop the statue in the middle.)

There were two more metaphorically significant activities that Tom had to do, in order to erase the pain of the break-up.

2. The second task is termed “overcoming meanness harmonically.” Tom had to wear Nicole’s ring and run a specified distance as fast as he could on a windy day. Then he had to dash back the other way, returning to his starting point. The condition he had to satisfy was this: his average speed on the two dashes, which both had to be done the same day, had to be higher than the fastest average speed that he could achieve if there had been no wind. “No problem,” thought Tom. He waited until he had a strong wind behind him, ran the distance and then ran right back. His fastest speed without the wind was 25 feet per second. With the wind behind him, he achieved 30 feet per second. On the way back, his speed was 20 feet per second. What was his average speed? How could he have done this right?

3. The third task is called “outsmarting frictional resistance.” Tom had to take an object associated with Nicole and toss it as high as possible into the air. Then he had to catch it as it fell down. The speed with which it was falling had to be higher than the speed at which it was thrown.

Now it is clear that if an object is thrown up at a certain speed and then it falls down under the influence of gravity, its speed when it reaches the point from which it is thrown will be exactly the same as on the way up if there were no air resistance. However, in real life, air resistance causes a frictional force that is proportional to the object’s speed at every point. On the way down, will the actual speed of the object at the starting point be the same, or higher or lower than it was on the way up? How can Tom Cruise satisfy the third task?

here is the puzzle online

The science of Avatar

Here are a few posts that describe the physics of the movie Avatar. In your lifetime, scientists have already discovered hundreds of extrasolar planets orbiting stars throughout the Milky Way (the first extrasolar planet was discovered in 1992).

The science of Avatar

Pandora could be a reality

More science of Avatar

Curious about how we discover extrasolar planets? Here's how.

You can even play a game to discover them on your own.