5.1 Temperature

Back in Physics 9A, the idea of thermal energy first arose in the context of energy conservation. We concluded that work done by non-conservative forces would convert mechanical energy into this form of energy, which became internal to the system, and didn't spontaneously return to mechanical form. We know intuitively that this form of energy reveals itself to our senses through temperature. We also can intuit that two objects at different temperatures that are brought into contact can exchange energy an change their temperatures (cold milk added to hot coffee both cools the coffee and warms the milk).