Suggested languages for you:

Americas

Europe

Q4 CQ

Expert-verified
Found in: Page 186

### College Physics (Urone)

Book edition 1st Edition
Author(s) Paul Peter Urone
Pages 1272 pages
ISBN 9781938168000

# When you push a piece of chalk across a chalkboard, it sometimes screeches because it rapidly alternates between slipping and sticking to the board. Describe this process in more detail, in particular explaining how it is related to the fact that kinetic friction is less than static friction. (The same slip-grab process occurs when tires screech on pavement.)

Kinetic friction acts when there is a relative motion between the surfaces. Static friction works if there is tendency of motion but no relative motion between the surfaces.

Kinetic friction acts when we are writing on the board while static friction works if we stop writing.

See the step by step solution

## Definition of Kinetic friction

Kinetic friction is the friction that occurs when two or more things are moving in opposite directions.

## Determining kinetic friction is less than static friction

Chemical bonding occurs between both the surface and the chalk when you push a piece of chalk throughout a chalkboard.

This bonding is responsible for static friction as well as kinetic friction. The friction force depends upon the nature of surface. Normally the coefficient of kinetic friction is less than static friction. The friction force is determined by the type of surface. Kinetic friction normally has a lower coefficient than static friction.

Therefore, value of kinetic friction is less the value of static friction.

While writing on the chalkboard there is a relative motion between the surfaces so kinetic friction works and lesser force is required to move the chalk.

But when the chalk sticking on the board static friction acts between the surfaces and it oppose relative motion so you require slightly greater force to write on the board.