 When I drop a ball, I normally say that the ball falls because of gravity. In actuality, the ball falls because it's reducing its potential energy. You've probably seen the warning labels on the back of a microwave popcorn bag about being careful of hot steam when you open the bag. You may have noticed that when you pour rubbing alcohol on your skin, the alcohol evaporates and feels cool. As the alcohol evaporates, it increases its potential energy and it removes energy from your skin. In chapter 11, you're going to learn about kinetic and potential energy. You're going to learn about the energy associated with different phase changes. You'll also learn how to predict which physical states will be present at certain conditions of temperature and pressure.