* Kinetic Energy: Heat is a form of energy. When you heat a substance, you are transferring energy to its molecules. This energy increases the molecules' kinetic energy, making them move faster and vibrate more vigorously.
* Spacing: As the molecules move faster, they collide with each other more frequently and with greater force. This increased motion causes the molecules to push each other further apart, leading to an overall expansion of the substance.
Think of it like this: Imagine a bunch of people standing close together in a room. If they start moving around and bumping into each other, they'll naturally spread out to give themselves more space. The same principle applies to molecules in a substance.
