 One of the physical properties that is determined by intermolecular forces is volatility or vapor pressure. If we take a substance like acetone and we pour a small amount on the table and wipe it away, you can see how quickly it vaporizes. Changes from a liquid to a gas. It appears to disappear. That's because of the attraction between one molecule of acetone and another. The intermolecular forces are weak, therefore it doesn't take much energy at all for them to change from a liquid to a gas. Let's look at water in the same way. We put a drop, a few drops of water. We wipe it away. You know from experience that it's going to evaporate, but it's going to take a lot longer than the volatile acetone.