Physics 105, Fall Term, 2009
Did you complete the reading assignment?
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?
Static friction is larger than kinetic 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)
It does not dissappear, it is transfered into heat and sound.
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Was there anything that you didn't understand in the reading assignment?
What was confusing to you?