1. The problem statement, all variables and given/known data Crewed spacecraft are equipped with heat shields for protection when they re-enter the Earth's atomsphere. Why is this necessary? 2. Relevant equations none 3. The attempt at a solution Because upon reentering, the speeds can get so high that the outside of the spacecraft can get very hot due to kinetic energy converting to heat energy. How does that work? It is hard to imagine? Should I imagine the atoms on the outside of the surface all moving at the speed of the craft so every atom is travelling extremely fast. However, heat is caused by collision of atoms. So collisions must occur. What about the air molecules colliding with the surface of the ship? Would that be the main cause of heating up the ship?