Rolling friction refers to the much smaller frictional force experienced by a round object rolling over a surface. Fluid friction refers to air resistance and the motion of objects in liquids.
Coefficients of Friction
surface | kinetic | static |
| wood on wood | .2 | .4 |
| ice on ice | .03 | .1 |
| steel on steel | .3 | .6 |
| rubber on solid | 1 | 1 to 4 |
| aluminum on steel | .5 | .7 |
| copper on glass | .5 | .7 |
| glass on glass | .4 | .9 |
- What is the direction of the force of kinetic friction relative to the motion of the object?
- Suppose that your car is stuck on ice. The wheels spin, but the car doesn't move. Your friend suggests that you let the air out of the tires to increase the amount of friction. Does this make any sense?
- Try to provide a molecular theory which explains why kinetic friction is less than static friction.
- As an object initially at rest on a horizontal surface is set into motion, the force of friction between them decreases, increases, remains the same.
- An empty wooden crate is slid across a warehouse floor. It the crate were filled, the coefficient of kinetic friction would between the crate and the floor would increase, decrease, or remain the same. What about the force of kinetic friction?
- A wooden block is at rest on a wooden inclined plane. As the angle the plane makes with the horizontal increases, the coefficient of static friction between the block and the plane decreases, increases, remains the same. What about the force of static friction?