Key Concept: Static
Understand the variable nature of static friction and the meaning of
the static friction force.
Objectives 1-4. Note that the mathematical model for static
friction calculates the maximum value and that there is no effect
from surface area.
5.1: Special pipe with rough and smooth surface - object:
Friction is a highly complex phenomenon. Simple explanations like
surface roughness do not explain it.
5.2: Attach a large spring scale to a weight on a table and
pull it horizontally. Do not allow the weight to move. For each
reading of the scale ask what the static friction force is. -
object: static friction force adjusts to match the pulling force.
5.3: C-clamp and wood block - object: increasing normal
force increases the maximum static friction force.
In Class Problem Solving:
- Jeb's flat bed truck accelerates
with his dog Blue in the back.
- Jeb slams on the brakes with Blue
on the roof.
5.4: Place a heavy object on a piece of paper and slowly
pull on it. The weight moves with the paper. Jerk the paper quickly
and the paper moves but the weight stays in virtually the same
location. - object: An object resting on a second object will
accelerate at the same rate as the lower one only if the friction
force is sufficient.
pipe with rough and smooth surface, C-clamp and wood block, video