why do molecules move faster as they heat up?

Answer 1

The act of molecules moving faster is what raises the temperature of an object. As you apply energy to a system (heating it) you are raising the potential energy of the system and the only way this can happen is if the molecules vibrate faster. When you remove the heat source the vibration slows down and the substance gives off energy (temperature drops) as it cools down.

It is no different that picking a weight up off the floor. When you do this you apply energy to the system and it exists in the form of potential energy (the weight being a certain distance off the floor). If you nudge it off the table it falls (potential energy converts to kinetic energy) to the floor and you get back the energy you put into the system (ignoring friction and all that).

Answer 2

They are cold blooded like snakes ;)

Don't think of it as why do they move faster when hot, think of it as why can't the move as fast when cold. Heat is energy. Molecules need energy to move. When they are very cold they simply don't have enough energy to move. The more energy you give them, the more they can bounce around.

Answer 3

because you increase their average kinetic energy (which is temperature).

Answer 4

Because it is hot.