# Temperature is the measure of average kinetic energy of an object

1. May 30, 2005

### primarygun

Temperature is the measure of average kinetic energy of an object.
If I put a thermometer in a pencil case, and I throw the pencil case away, the reading does not change. However, the kinetic energy of any particles of the pencil case did vary. Why?

2. May 30, 2005

### IntuitioN

The effects are negligible...?

I'm not too sure what you meant by throwing it away.

3. May 31, 2005

### primarygun

Increase its speed;

4. May 31, 2005

### whozum

The average kinetic energy of the molecules is barely affected by the throw.

5. May 31, 2005

### primarygun

why? ??
The speed of the object increased

6. May 31, 2005

### whozum

But the average kinetic energy of each individual molecule is approximately the same.

7. May 31, 2005

### SpaceTiger

Staff Emeritus
Note also that temperature is used to describe an object in thermodynamic equilibrium. If all of the atoms and electrons are moving at the same velocity, then the energy is not equally divided among the degrees of freedom. Thus, this would not be well described by a "temperature". You could, however, describe the energy as a linear combination of a total translational kinetic energy and a thermal energy with the same temperature as that measured at rest.

8. May 31, 2005

### dreamfly

& if you want to measure its tempreture,the thermometer would fly with it,therefore there'll be no kinetic energy to the thermometer,so the figure will retain the same,isn't it?

9. May 31, 2005

### DaveC426913

The speed of the moving pencil case is negligible compared to the speed of the atoms flying around.

10. May 31, 2005

### SpaceTiger

Staff Emeritus
That's another good point. Since physics is invariant under Lorentz transformations (in other words, we switch to a frame moving with the thermometer and case), then a throw at a constant velocity in a vacuum should give the same temperature measurement as at rest. In real life, though, there would be air drag and friction forces dissipating the kinetic energy of the case and thermometer, effectively thermalizing the energy. Thus, if you throw it fast enough, you will eventually notice a change in temperature (don't forget that fast-moving objects will often "burn up" in the atmosphere).