1. The problem statement, all variables and given/known data In which of the following cases does the internal energy of the described system increase: (I) A clay ball is dropped and sticks to the ground (II) Hydrogen and oxygen react exothermically to form water (III) A car is driven at constant speed (consider the effect of air resistance) 2. Relevant equations NA 3. The attempt at a solution When I look at I and III, I think of kinetic energy and potential energy (if elevated). But then when I think of internal energy, I think chemical reactions. How can a macroscopic object such as I and III have an increase in internal energy?