Fact 1: Friction causes an object to lose energy.

Fact 2: Friction occurs when two substances rub together.

Given the two facts above, answer the question "what causes an object to lose energy" with the following options: 
- wind and erosion
 - pressure differences.
 - refract or absorb.
 - heat is produced
 - electron transport
 - depress neuronal excitability
 - degrees Celsius
 - 2 substances rubbing together


 

        2 substances rubbing together 