Antoms
The atoms that make up the matter begin to move.
faster
You can raise an object (potential energy), make it move (kinetic energy), or add heat to it (heat energy, a.k.a. thermal energy).
heat
faster. and matter then would move slower
faster
They move faster.
If you add heat to matter, it can either get it hotter, or it can change the state of matter (for example, from solid to liquid).
faster. and matter then would move slower
When heat is added to a pure phase of matter, the kinetic energy of the particles in that phase increases. This increase in kinetic energy causes the particles to move faster and the temperature of the phase to rise.
That depends a lot on how the particle was moving in the first place, and how the energy is added.
By radiation. Only conduction and convection need a medium in which to move