## Due 3:30 pm, Tuesday, September 22nd

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) Friction is a nonconservative force.

2) The force of friction is a result of the normal force and the coefficient of friction of the object.

3) Each object has a coefficient of static friction and a coefficient of kinetic friction, with the coefficient of static friction being greater in all cases.

Go to the following applet: http://phet.colorado.edu/sims/forces-1d/forces-1d_en.jnlp. It should look familiar to you.

Put the barriers up by clicking on the 'Barriers' check box again, but this time leave the friction setting on.

Slowly increase the amount of force that you put on the file cabinet by until it starts to move and note the net force acting on it. Then slowly decrease the amount of force you apply to it while it is moving. Does it take more applied force to move the file cabinet before it starts moving or after it is already moving?

Before it is moving
After it is moving

The answer above is a result of what property of friction?

Now apply a large force to the cabinet for a short moment by clicking on it and quickly dragging it with the mouse to the right or left and then releasing the mouse. Does the file cabinet appear to be keeping Newton's 1st law?

Yes, the cabinet remains in motion.
Yes, the cabinets change in motion is the result of a force acting on it.
No, the cabinet does not stay in motion.
No, the friction force is nonconservative.

Frictional force is considered a nonconservative force because it dissipates, or decreases and no longer affects an object when it stops. What would happen to the cabinet if the friction force did not dissipate after you stop pushing it?

It would go on forever in the direction that it was pushed.
It would change direction and start moving in the opposite direction of how it was pushed..
Nothing would change from what was observed.

With this nonconservative force dissipating, does it disappear? What happens to it? (If you don't know, create friction between your hands by rubbing them back and forth really fast and observe what happens)

FEEDBACK

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?