Any stimulus that, when presented after a response, strengthens the response is called a(n)

This would be a positive reinforcer. These are things like rewards and bonuses that will cause the subject to want to continue the rewarded behavior. The reinforcer does not need to be financial or even tangible. Positive comments and approval can be reinforcers that strengthen associated behaviors.

Silicon is cut into tiny pieces for computer chipslead is melted to form pelletsliquid water freezes to form ice

Gravitational force i believe