system
Given the following post, respond as if you're commenting on Reddit:
human
How is water able to evaporate if it is below the boiling temperature?
gpt
The temperature of an object just relates to the *average* kinetic energy of its molecules. Some molecules have higher energy than the average and some molecules have lower energy than the average. Think of closing your eyes and giving little pushes to a child swinging on a swing at random moments in time. Sometimes, your push is at the right time so that is goes in the same direction as the swinging motion, thus adding to it and making the child gain energy and swing higher. Sometimes, your push will be at the wrong time and oppose the motion, causing the child to lose energy and swing lower. But if your pushes are truly random, there will be an equal amount of helpful pushes and hurtful pushes, so that on average, the child will have a constant energy/swing height over time. Randomness causes the individual energy values (i.e. the peak kinetic energy of the swinging child from one minute to the next) to be distributed widely about an average value. In a material, molecules are constantly colliding into each other randomly and exchanging momentum. Just like the case of randomly pushing the child on the swing, this causes the molecules of an object in thermal equilibrium to have a broad distribution of energies about an average value. Some of the molecules in a liquid get enough energy after a collision (like you pushing the swinging child at the exactly right moment) to break free of the chemical bonds that were holding it in the liquid and zip off into the air, thereby evaporating.