Here’s a nice, simple graphic showing the motion of particles in a gas. Some are moving faster, some slower; the average velocity is a function of the temperature.

Here’s the caption from the Wikipedia article on temperature:

The temperature of a gas is a measure of the average kinetic energy of its atoms or molecules as they move and collide. Here in this animation, the size of helium atoms relative to their spacing is shown to scale under 136 atmospheres of pressure. These room-temperature atoms have a certain, average speed (slowed down here two trillion fold).

I like the graphic because it is simple, yet it clearly communicates the concepts of transfer of kinetic energy from one particle to another, and average speed.

Grace and Peace