11/18 physics update and homework due 12/2

Hi folks,

Today we went did another fairly complex lab where I had the students find acceleration, terminal velocity, gravitational force and friction force of a system using a ball and a ramp.  The students had to really think about all the formulas we've been using, as well as think about last week's lab.  It was quite a mind bender and they did a great job.

Homework for 12/2 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.