Heat Loss & Mass: Kinetic Theory Explained

• Antigone
In summary, the kinetic theory of matter explains that all matter is made up of constantly moving atoms and molecules. When heat is added to a substance, the molecules and atoms vibrate faster, causing the space between them to increase. This motion and spacing determines the state of matter. When heat leaves a substance, the molecules vibrate slower and the atoms can get closer, resulting in the matter contracting. This change in molecular motion also affects the mass of the object, but the amount of mass lost or gained is so small that it is typically ignored. Heat is not made up of photons, but it can be emitted as thermal radiation in the form of electromagnetic waves. Finally, it is important to note that while most substances expand when heat is added
Antigone
Hi

Qoutation:

"Kinetic theory of matter: All matter is made up of atoms and molecules that are constantly moving.

When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space.

Mass of the object remains the same, however. Solids, liquids and gases all expand when heat is added. When heat leaves all substances, the molecules vibrate slower. The atoms can get closer which results in the matter contracting. Again, the mass is not changed."
I am just wondering: If matter loses heat, it loses photons (because heat is made up of photons). But if it is loosing energy, how come it isn't losing mass? What happened to E=mc2, where energy is a form of mass?

Electrons lose energy because of the resistence in different materials. This energy comes out as heat. Why would matter not lose mass when losing heat (energy)?PS. The name of the website is https://www.mansfieldct.org/Schools/MMS/staff/hand/atomsheat.htm

It does lose mass when it loses heat. If everything else is identical, a colder object has less mass than a hot one. The amount of mass lost or gained is so small that we typically ignore it though. That's probably why that site is saying the mass doesn't change.

Antigone said:
I am just wondering: If matter loses heat, it loses photons (because heat is made up of photons). But if it is losing energy, how come it isn't losing mass? What happened to E=mc2, where energy is a form of mass?

You are right, an object loses mass according to ##E=mc^2## as it cools. This effect is so small that it is generally completely ignored, and that's what the source you're citing has done.

(Although not directly relevant here, heat is not made up of photons and a cooling object does not necessarily give up its energy by emitting photons. That's one way it can happen, but not the only way)

Nugatory said:
You are right, an object loses mass according to ##E=mc^2## as it cools. This effect is so small that it is generally completely ignored, and that's what the source you're citing has done.

(Although not directly relevant here, heat is not made up of photons and a cooling object does not necessarily give up its energy by emitting photons. That's one way it can happen, but not the only way)

I believe heat can come in a couple of forms. But when I say heat consists of photons I mean in the sense of thermal radiation.

From Britannica:

thermal radiation, process by which energy, in the form of electromagnetic radiation, is emitted by a heated surface in all directions and travels directly to its point of absorption at the speed of light; thermal radiation does not require an intervening medium to carry it.

Thermal radiation ranges in wavelength from the longest infrared rays through the visible-light spectrum to the shortest ultraviolet rays.

Here is the link: http://www.britannica.com/EBchecked/topic/591461/thermal-radiation

Therefore heat is made up of photons, when it is a electromagnetic radiation (thermal radiation).

Drakkith said:
It does lose mass when it loses heat. If everything else is identical, a colder object has less mass than a hot one. The amount of mass lost or gained is so small that we typically ignore it though. That's probably why that site is saying the mass doesn't change.

Strange that they would teach a false statement to students. If it does lose mass, then it is false to say that it doesnt.

Thank you, I was quite frustrated there for a while.

No, heat is not made of photons. Just because a hot object emits photons doesn't mean it's made of photons. A skunk emits stink but a skunk is not made of stink.

Antigone said:
Strange that they would teach a false statement to students. If it does lose mass, then it is false to say that it doesnt.

Thank you, I was quite frustrated there for a while.
Because it is impossible to teach kids everything simultaneously, it is necessary to include simplifications. Just be aware of that and don't let it frustrate you: They aren't trying to mess with you, they are just trying to control the torrent of information thrown at you at once.

I just want to point out that it is possible for a substance to actually shrink instead of expand when heat is added. Water does that in the temperature range from 0°C to 4°C

Antigone said:
PS. The name of the website is https://www.mansfieldct.org/Schools/MMS/staff/hand/atomsheat.htm

Antigone said:
Strange that they would teach a false statement to students. If it does lose mass, then it is false to say that it doesnt.

Please note that this site was created by the teacher of an 8th grade general-science class in the USA. So it's intended for 14-year-olds, who have not even started high school yet; and it's written by someone who is not a professional textbook author and probably has a degree in chemistry or biology rather than in physics.

I think it would be rather unusual to discuss relativity in a general-science class at this level in the USA. Maybe in some other countries...

1. What is heat loss?

Heat loss is the transfer of thermal energy from a warmer object or substance to a cooler one. This can occur through conduction, convection, or radiation.

2. How does heat loss affect temperature?

Heat loss can cause a decrease in temperature since it removes thermal energy from a substance. This is why objects cool down when left in a colder environment.

3. What is the kinetic theory of heat and mass?

The kinetic theory of heat and mass explains that the temperature and pressure of a gas are determined by the average kinetic energy of its particles. It also states that the total mass of a system remains constant, but the distribution of the mass can change as particles move and collide.

4. How does the kinetic theory explain heat loss?

The kinetic theory explains heat loss by stating that as particles in a substance move and collide, they transfer thermal energy to each other. This transfer of energy results in a decrease in temperature and ultimately leads to heat loss.

5. What factors affect the rate of heat loss?

The rate of heat loss is affected by the temperature difference between the warmer and cooler objects, the thermal conductivity of the materials involved, and the surface area and thickness of the object. Other factors such as wind speed and humidity can also impact the rate of heat loss.

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