Sec 3.3 - Friction

1
21.1
Sec 3.3 - Friction
Read p 83-86
Friction Force that opposes the sliding motion
of two surfaces that are in contact.
All surfaces have bump and dips.
When surfaces come together, bumps and dips
touch each other.
2
21.2
When surfaces come together, bumps and dips
touch each other.
Creates microwelds, making surfaces
stick together.
3
21.3
What if force applied?
Force
Presses bumps closer, creates more friction.
4
21.4
Static Friction Forces that prevent surfaces in
contact from sliding past
each other.
applied force
static friction
Velocity of box 0 (no movement)
5
21.5
Sliding Friction Forces that act in opposite
direction to motion of
surface sliding.
Must overcome static friction
applied force
sliding friction
Velocity of box gt 0 (movement)
6
21.6
Air Resistance Frictional force that opposes
motion of objects that
move through air.
Which falls faster?
What if they fell in a vacuum (no air)?
Fall at same rate, no resistance.
Amount of air resistance depends on type
and shape of the object, not the mass (weight).
7
21.6
Force of air resistance
Force of gravity