Here's why:
* Heat is the transfer of thermal energy. Thermal energy is the internal energy of a system due to the random motion of its atoms and molecules.
* Collisions transfer energy. When atoms or molecules collide, they exchange kinetic energy. This exchange can be from a hotter (higher energy) molecule to a cooler (lower energy) molecule.
* Conduction is the transfer of heat through direct contact. This direct contact allows for these collisions to happen, transferring energy from one molecule to another.
Think of it like this: Imagine a line of people holding hands. If one person at the end of the line starts shaking, the energy of that shaking will travel down the line through the chain of hand-holding collisions.
