Transcript:

So, let's look at mass and temperature. We think that mass and temperature are properties of a given object. An object has a mass, and an object has a temperature, but it's not so straightforward. Here's why.

You take that same object, and you cut it in half. The mass of it becomes half, but the temperature remains the same. So far, so good. But if you take it to the extreme, you go down to one particle of that thing. It has a mass, but that one particle of this thing has no temperature. You cannot define a temperature of one molecule or one atom.

Temperature is defined only for a large collection of things. Temperature is what is called an ensemble property. "Ensemble" is a French word that means "collection." Temperature is an average of the collection of particles that gives a representation of how fast those particles are moving. That's all it is. Temperature is simply an average of how fast the particles are moving. An individual particle does not have a temperature.