The expansion of a liquid is greater than the expansion of a solid.

Picture a liquid, where the molecules are moving about freely, and more quickly than in a solid. As you’ve learned, the shape of a liquid depends on the shape of the container it is in.

Getting back to our analogy, if you have a roomful of people (the liquid) all moving about freely, and you warm them up so they now move about faster, they will bump into each other and bump off the walls. The walls of the room still hold them in, however. The only direction they can move to “expand” and move more freely is up! Some will start jumping up and down, and in this way the liquid is expanding. The molecules in a liquid are free to move and expand more than in a solid.