Final answer:
The screeching sound made by chalk on a chalkboard is a result of it alternating between sticking due to static friction and slipping due to kinetic friction. This demonstrates that static friction is greater than kinetic friction, as static friction must be overcome to start movement and is stronger than the friction experienced once the chalk is moving. The correct answer to the question is b) Static friction prevents slipping; kinetic friction allows slipping.
Step-by-step explanation:
When you push a piece of chalk across a chalkboard and it makes a screeching sound, this is due to the chalk rapidly alternating between sticking to the board and slipping over it.
This happens because static friction, which prevents motion between surfaces at rest, is greater than kinetic friction, which occurs once the surfaces are in motion. Specifically, when you push the chalk, static friction keeps it from moving until you apply enough force. Once the force exceeds static friction, the chalk moves (slipping), and kinetic friction takes over, which is less than static friction. The noise occurs because this slip-stick cycle repeats rapidly.
An analogy is trying to slide a heavy crate across concrete; it's difficult to start moving due to static friction but gets easier once it's already in motion because of lower kinetic friction. Adding weight to the crate or lubricating the surface with oil affects both static and kinetic friction but does not change the fact that static friction is generally stronger than kinetic friction.
Given the options:
- a) Kinetic friction is stronger than static friction.
- b) Static friction prevents slipping; kinetic friction allows slipping.
- c) Kinetic friction is unrelated to slipping.
- d) Both static and kinetic friction prevent slipping.
The correct option that describes the relationship between static and kinetic friction is b) Static friction prevents slipping; kinetic friction allows slipping.