Friction Flashcards
What does friction resist
Sliding of two bodies
What is dry friction and what is it proportional to
No lubricant between bodies
Proportional only to Nc
Three rules of dry friction
1) contact forces occur in equal and opposite pairs
2) contact forces are not generated at all points of contact
- depends on the relative motion of the two surfaces
3) contact forces are perpendicular to the contact point
- for perfectly smooth surfaces (not real): only the vertical contact force exists
Why doesn’t a box start moving initial when u push it
Friction is just enough to resist sliding but no more
What is impending motion
Box on verge of sliding
What does tipping arise from and what is it dependent on
Arises from impending motion and no sliding
Dependent on geometry
What causes tipping before sliding
If overturning moment is sufficient, body could tip before it slides
When is the max possible frictional force
When box is on the verge of sliding
What is the angle of repose and what is it always the same as
Angle of an incline required for box to start sliding
Same as angle of static friction
Friction is _____ to the surface contact
Tangential
Friction is independent of ____ ___
Contact area
Equation for impending motion
F = Us(N)
Equation for sliding
F = Uk(N)
Which direction is frictional force when wheel has a concentrated FORCE
Friction opposes concentrated force
Which direction is frictional force when wheel has a concentrated MOMENT
friction is in the same direction as moment
