In other words, what happens at constant temperature when we take a balloon filled with air and squeeze it. Well, we said that, and Boyle's Law explained this, that when we squeeze the balloon, we decrease volume, increase pressure, and eventually our balloon will pop. Now we're going to look at another law called Charles Law which also helps us explain the macroscopic large scale behavior of many gas molecules and how they interact with one another and with our system. So for Charles Law to work, two conditions must hold. We must have constant pressure and we must have constant number of molecules. So our N number of moles stays the same.