Fill in the following three physical quantities: heat, temperature and internal energy: (1) It is very hot today, and "heat" means _ _ _ _ (2) friction.

(1) Today, the weather is very hot, which reflects the degree of hot and cold objects, so this "hot" refers to the temperature;

(2) Friction generates heat by overcoming friction, so "heat" here refers to internal energy.

(3) Water absorbs heat and heats up. Here "heat" refers to the heat absorbed in the process of heat transfer, so "heat" refers to heat;

(4) Fuel combustion generates heat, and "heat" refers to internal energy.

So the answer is: temperature; Internal energy; Heat; Internal energy