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.