1. The problem statement, all variables and given/known data Why is heat energy unusable? 2. Relevant equations Heat = total kinetic energy of an object 3. The attempt at a solution I've come across this statement so many times - whether it be in Physics, Environmental Science, Chemistry, or Biology - "thermal energy (heat) is unusable." What makes heat energy unusable? Why can't it be harnessed? I read that heat is unusable in cells because the temperature in cells are fairly even throughout. Can someone please explain what that means, and also explain why exactly heat is considered "unusable"?