# Whenever energy is added to a system, the system gains mass

• dav2008
In summary, according to the Wikipedia page on mass-energy equivalence, whenever energy is added to a system, the system gains mass. This is demonstrated through examples such as a compressed spring, where the added potential energy increases the mass, and an object's temperature, where an increase in heat energy also increases its mass. However, there may be some debate about the effects on mass when lifting a box or changing its gravitational potential energy.
dav2008
Gold Member
"Whenever energy is added to a system, the system gains mass"

http://en.wikipedia.org/wiki/Mass-energy_equivalence#Practical_examples
From wikipedia:
Whenever energy is added to a system, the system gains mass. A spring's mass increases whenever it is put into compression or tension. Its added mass arises from the added potential energy stored within it, which is bound in the stretched chemical (electron) bonds linking the atoms within the spring. Raising the temperature of an object (increasing its heat energy) increases its mass. If the temperature of the platinum/iridium "international prototype" of the kilogram — the world’s primary mass standard — is allowed to change by 1°C, its mass will change by 1.5 picograms (1 pg = 1 × 10–12 g).[8]

Is this actually true? If someone said this to me in a conversation I would tell them compressing the spring does absolutely nothing to its mass and increasing the temperature of an object does nothing to its mass.

Now it's on Wikipedia so I'm wondering if I'm missing some concept here...

I was going to remove it but I wanted confirmation first.

The temperature example sounds plausible, but I don't know about the compressed spring. By that same token of logic, if PE increases mass, lifting a box will increase the mass?

Temperature I can get because of the motion of the particles etc. but nothing fundamental changes about a box when I lift it 1m, giving it gravitational potential energy.

Nabeshin said:
if PE increases mass, lifting a box will increase the mass?

I gave an answer to this question in the following thread just a few minutes ago:

dav, did you bother to read the reference ("[8]") for the paragraph you wish to delete (from the wikipedia page on a topic that you don't understand)?

Yes, compressing a spring or heating a potato increase their mass. (Hint: in one sense we can say that energy is mass, and nobody disagrees with this when we are referring to a system that is at rest.)

Lifting a box higher above the Earth can increase the mass of a system encompassing both the Earth and the box, but not of the box itself (as Nabeshin and jtbell noted).

## 1. How can energy add mass to a system?

According to Einstein's famous equation E=mc², energy and mass are two forms of the same thing. When energy is added to a system, it increases the mass of the system by a small amount.

## 2. Is the mass gained by a system when energy is added permanent?

Yes, the mass gained by a system when energy is added is permanent. This is known as the conservation of mass-energy, which states that energy cannot be created or destroyed, only converted from one form to another.

## 3. How does adding energy to a system affect its mass?

Adding energy to a system increases its mass by a small amount, as determined by Einstein's equation. This is because energy has a physical presence and therefore contributes to the overall mass of the system.

## 4. Can adding energy to a system also decrease its mass?

Yes, adding energy to a system can also decrease its mass. This is known as mass defect and is seen in nuclear reactions, where a small amount of mass is converted into a large amount of energy.

## 5. Does the type of energy added to a system affect its mass gain?

No, the type of energy added to a system does not affect its mass gain. All forms of energy, whether it be thermal, kinetic, or potential, contribute to the overall mass of the system in the same way according to Einstein's equation.

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