Laws of thermodynamics

There are three laws of thermodynamics.

1. Energy is neither created nor destroyed. It's all in a closed system, that system being the universe itself. Let's say you're about to drop a ball. The ball has energy—potential energy—and when it falls, that potential energy is converted to kinetic energy. From a mathematical perspective, the change in internal energy, $\Delta U$, equates to the heat added minus the work done by the system.
2. Heat, of course, flows from a hot body to a cold body. Think of a silver spoon. It's at room temperature. You put it in a pot of boiling soup and stir it, and suddenly it's hot. Apparently the use of a time machine violates this law, despite time machines not necessarily relying on heat.
3. The entropy of a system at equilibrium becomes more and more constant as the temperature reaches absolute zero. This is where we get Heat Death of the Universe.