The number of molecules in some water isn't affected by changing its temperature. But to know if you have the same number of molecules in two water samples, you need to compare their masses, not their volumes. When you heat some cool water, it expands. (When you slightly warm some ice-cold water, it contracts a little, but let's keep this simple.) So hot water takes up more space than cold water. The amount of space something takes up is called volume. If you were to have 2 cups of water, one of hot water and one of cold water with equal volumes, the cold water would have more molecules.
<span>Hot and cold water are made of the same type of molecules. Each molecule has one oxygen and two hydrogen atoms. The difference between them is the speed of the molecules jiggling around. </span>
Ice, less friction, glossy and slippery etc. When ice skating, the fast movement actually temporarily melts the ice because of all the friction. Dense molecules
Water, lots of resistance. It's very dense so it's harder to move through. Molecules move around freely to fit their space.
Air, not very dense at all, easy to move through since it's light and molecules are spread out the most.
