Fwd: 1/13 Physics update and HW due 1/20

Hi folks,

Today we spent time pushing my van around.  No, I wasn't out of gas.  This was a great way to get the students more familiar with Newton's 2nd Law.  By pushing the van, the students were actually able to be the force that accelerated the mass of the vehicle.  We also had teams of students push and noticed that the more force that was applied, the more acceleration there was.  Each student was able to figure out the amount of force they put on the van by figuring out the velocity (d/t), then the acceleration (v/t)  and then the force applied f=ma.

Homework for 1/20 is to use the Phet simulation Forces and Motion to answer the following questions.

Here's the link http://phet.colorado.edu/en/simulation/forces-and-motion

Click on the picture of the crate and drag to the right.  Notice that as you do there are two force vectors.  One is for the force the man is applying and the other is the friction force.  

1.  What happens to the friction force the second the crate begins to move?  Why?

2.  What is the minimal amount of force you need to apply to get the crate, filing cabinet, sleepy dog, refrigerator, and textbook to move?   (You may want to use the "Applied Force" slider for this.)  How does this relate to mass?

3.  If you stop applying force to any of the objects what happens on wood?  How about on ice? (Use the radio buttons in the upper right hand side to switch.)  Describe what's happening there using Newton's First Law and then by using Newton's Second Law.

4.  Click on the radio button for sum of forces.  What is that green arrow showing?

Click on the "Friction" tab at the top of the screen and do the following questions.

5.  What happens to the pushed objects as you increase and decrease the amount of friction?

6.  What happens to the Fg and the Fn if you change the gravity?

7.  What happens to the Fg and the Fn if you change the object mass?

Click on the Force Graphs tab at the top of the screen for the following questions.  Click on the acceleration and velocity buttons in the bottom right to bring up those graphs.

8.  Mess with the forces a bit and then draw all three of the graphs that was created by something you tried.  Label the graph at any location where change took place.  Notice the correlation between force, acceleration, and velocity.

9.  Turn "ice" on and draw another three labeled graphs.  

10. With "ice" and "bouncy walls" on draw another 3 labeled graphs.