In this first simulation, there is no attraction between particles. Following Newton’s three laws of motion, the particles move at a constant velocity until they collide with a wall or another particle. Use the slider to adjust the speed of the particles.
As you can see, the particles do not clump together, even when the particle speed is very slow. We know that particles that do not interact will never enter a liquid state because, by definition, they would form an ideal gas. The theory that non-attracting particles will condense into a liquid state when particle speed decreases is utterly nonsensical. The theory is ungrounded, does not scale, and cannot be leveraged to explain any other liquid phenomena.
However, if we give the particles a bit of attraction—as in the second simulation—the particles start behaving like tiny magnets and do clump together. Notice that, even though particles are attracted to one another and clump at low speeds, the particles never stop moving. In fact, these particles keep moving even when we set the particle speed to zero. That happens because the slider is only setting the initial speed of the particles. Once the simulation is running, particles will accelerate toward each other because of the attractive forces, converting potential energy into kinetic energy.
By turning the particles into tiny magnets, the theory that particles will condense into a liquid state when particle speed decreases now makes sense. I believe this theory can be grounded—even for young children, it can be scaled, and it can be leveraged to understand phase transitions, solubility, characteristic properties of substances, cell chemistry, and much more.