08-05-2012, 02:53 PM
Net Forces, Friction, Air Resistance
08_friction.ppt (Size: 378.5 KB / Downloads: 173)
Recall the Sliding Book Example
Why do things not continue to move at constant velocity?
Don’t things strive to be at rest (I know I do)?
If the sliding book slows down, what’s the force responsible?
How could I keep it moving at a constant velocity?
Do I need to apply a force to keep it moving? Why?
Why Doesn’t Gravity Make the Box Fall?
Force from floor on box
cancels gravity.
If the floor vanished, the
box would begin to fall.
Some Questions
Does friction always exert a force that tends to bring things to a halt?
What does this say about the direction of the frictional force, relative to the velocity vector?
What do you think would happen if we loaded lead bricks into the box? Would it become harder to slide?
What are some ways to reduce frictional forces?