Explain what happens to the average kinetic energy, thermal energy, and temperature of a substance when the particles in the substance slow down.

the warmer substance because the particles are moving faster and farther apart

The particles in a substance slow down when the average kinetic energy of the particles decreases. As the average kinetic energy decreases, the internal energy decreases, and so the thermal energy decreases. As the thermal energy of the substance decreases, the temperature decreases.