Final answer:
Screeching caused by chalk on a chalkboard occurs when chalk rapidly alternates between sticking due to static friction and slipping with kinetic friction, which is less than static friction. Similar phenomena are observed with screeching tires on pavement.
Step-by-step explanation:
When you push a piece of chalk across a chalkboard and hear a screeching sound, you are experiencing the phenomena of slipping and sticking caused by the dynamics of static and kinetic friction. Initially, static friction prevents the chalk from moving until a certain threshold is passed. Once this threshold, where the applied force exceeds the static friction, is surpassed, the chalk slips, resulting in kinetic friction, which is less than static friction. The repeating pattern of exceeding and falling below this frictional threshold causes the piece of chalk to rapidly alternate between sticking and slipping, which produces the characteristic screeching sound.
The same principle applies to tires on pavement. When a tire rapidly alternates between gripping and losing traction on the road surface, often due to a sudden or forceful application of power or braking, it results in a screeching noise as the tire slips with kinetic friction and then catches again with static friction. This is because it's easier to keep an object moving (kinetic friction) once it has overcome the initial resistance to movement (static friction), leading to the irregular motion that generates sound.