When particles in a substance slow down, their average kinetic energy decreases. Kinetic energy is the energy of motion, and it depends on the mass of the particles and their speed. As particles move slower, their kinetic energy decreases. This is because they have less energy to move.

Thermal Energy:

Thermal energy is the total kinetic energy of all the particles in a substance. When particles in a substance slow down, their thermal energy also decreases. This is because the total kinetic energy of all the particles decreases.

Temperature:

Temperature is a measure of the average kinetic energy of the particles in a substance. When particles in a substance slow down, their average kinetic energy decreases, and so does the temperature. This is because temperature is a measure of how fast the particles are moving. As the particles move slower, the temperature decreases.