1. Jun 27, 2015

Tam Le

What do we mean when we say an object gained heat?

According to my understanding, heat is not a "thing" that an object can have: It is internal energy that is transferred from a hotter object to a colder object. In other words, it is an energy transfer process.

So, if an object gained heat, it must have received internal energy from a hotter object, right?

2. Jun 27, 2015

jfizzix

In short, yes.
However, it's still a little awkward to say that an object gains or loses heat.
Heat is not a substance that is created or destroyed,
it is just a form of energy measured in part by thermometers, calorimeters, and the like.

With the laws of thermodynamics, we can show that heat flows from hot (high-temperature) to cold (low temperature)
So yes, if an object received heat through a spontaneous process, it must have received that internal energy from a hotter object.
However, if you put additional work into the system, you can drive heat flow in the opposite direction. This is principle underlying refrigerators, air conditioners, and other such things.

3. Jun 27, 2015

Tam Le

Thank you jfizzix for replying.

However, if I understand correctly, you say that heat is a form of energy. But, can't an object possess/hold onto this "thing" called energy. Therefore, an object can possess/hold onto heat, which it should not be able to do.

4. Jun 28, 2015

jfizzix

What i said before could definitely stand to be made clearer:

An object has energy, which may take many forms, of either kinetic, or potential energy.

If you were to add up the kinetic energy of all the atoms making up an object, you would get a number much larger than $\frac{1}{2}m v^{2}$, where $m$ is the total mass, and $v$ is the speed of the center of mass.
The rest of that energy is tied up in the internal vibrations, and other jiggling. That bunch of kinetic energy can be considered heat (though there are other contributions to heat as well).

All things being equal, hotter objects have more internal kinetic energy per kilogram than colder objects. If a hot and cold object are brought together, energy can flow back and forth, as these internal vibrations can propagate from one material to another and back again. Over time, the distribution of internal energy is evenly balanced, and both objects have equal temperature. The reason that this happens is that it is by far the most likely random distribution of energy to occur. To have something different happen is about as likely as still air in a sealed room spontaneously becoming windy.

5. Jun 28, 2015

davenn

Heat can also be generated spontaneously internally without input from an outside source --- consider radioactive decay

Dave

6. Jun 28, 2015

Tam Le

Essentially, heat is a form of energy associated with an object's "internal vibrations, and other jiggling."

Now, if an object moves from point A to point B, it has translational kinetic energy. If an object were lifted up high relative to the earth, it has gravitational potential energy.
Yet, if I said that an object has heat, it is incorrect? Would saying "an object has heat energy" be the correct way?

7. Jun 28, 2015

jfizzix

I would say that the object has internal kinetic energy, or thermal energy, but I'm no authority on proper scientific terminology. That's just what I've heard/seen.

8. Jun 28, 2015

jfizzix

Radioactive decay is indeed a spontaneous process that releases heat.
Instead of energy being transferred from another object, it is energy transferred from different degrees of freedom within the same object.
Another example of a spontaneous process that creates heat would be an exothermic chemical process, like combustion/fire

9. Jun 28, 2015

rootone

Raising the object higher relative to the Earth gives it greater potential energy,it wont get hotter.
If the object falls back to Earth and impacts that potential energy will be released as heat.
(If it burns up in the atmosphere it amounts to much the same thing)

Last edited: Jun 28, 2015