Fact 1: Friction causes the temperature of an object to increase.

Fact 2: Friction in bearings causes an increase of the temperature inside the bearing.

Given the two facts above, answer the question "What increases the temperature of a bearing?" with the following options: 
- metal type
 - water
 - friction
 - Energy.
 - wind
 - speed
 - vaporization
 - energy


 

   friction      