# Can the mass of a body change under any condition or not? [closed]

We know that mass can neither be changed nor be destroyed, but I want to know if there is any circumstance under which the mass of a body can be changed?

• I'm voting to close this question as off-topic because it makes blatantly false claims. Apr 19, 2015 at 18:31
• Not to brag or anything, but I've lost 13.6 kg since December. I'm pretty sure that I'd consider that mass lost. Apr 20, 2015 at 2:39
• The accepted answer is not correct see here: "... The action of stretching the spring or lifting the mass is performed by an external force that works against the force field of the potential. This work is stored in the force field, which is said to be stored as potential energy." The mass of the body does not change at all.
– user77485
Apr 23, 2015 at 10:59

The mass of a body can be changed in accordance with Einsteins famous E=mc^2. Kinetic Energy for example adds mass to an object. This effect is not noticeable at everyday speeds but velocities approaching the speed of light change the mass of an object significantly. The effect can be named as part of the reason why particle masses are often given in electronvolts and supermassive particles such as the bottom quark obtain their masses throught their high velocities.

Actually, mass can be produced and destroyed (particles are produced and destroyed in high-energy collisions). It is popular to say in Chemistry courses that mass cannot be produced or destroyed. This is because the low energies encountered in chemical reactions (per atom chemical energy scales are of order 1 eV) are insufficient to produce anything new and anti-particles are typically not present.

Changing mass without producing or destroying it is not possible however. In relativistic language, the energy is different when we go to a different frame of reference (for instance, one in which the particle moves at high speed) but the mass is the "length of the energy-momentum 4-vector" and is invariant.

We know that mass can neither be changed nor be destroyed

It's energy that can be neither created nor destroyed.

I want to know if there is any circumstance under which the mass of a body can be changed?

Yes, heat it up and you increase the mass. Or lift it up, and you increase the mass. Then when you drop it, some of its mass-energy is converted into kinetic energy and gets radiated away. Then you're left with a mass deficit, see Wikipedia. Also check out mass in general relativity.

• That is not correct: PE is virtual energy that refers to the system, and is not stored in the body itself. When you lift a body its PE increases, but its mass does not.
– user78040
Apr 20, 2015 at 16:39
• @user77632: I'm afraid potential energy is physical, and it is stored in the body. When you lift a body you do work on it. You add energy to it. The Earth doesn't move, you do no work on it. Imagine you throw a brick up at 11.2km/s. As it slows down, kinetic energy is converted into potential energy. This is in the brick, nowhere else. It isn't in the Earth, or in the space between the Earth and the brick. It isn't in the gravitational field. And this brick has escape velocity, it departs the system taking all that energy with it. The Earth's gravitational field is diminished as a result. Apr 20, 2015 at 18:42

Sort of. When you make an object go fast, that is the speed close to the speed of light, requires more and more energy to accelerate. This is attributed to something called relativistic mass, but it isn't mass in the traditional sense, and thinking about it in the same way as mass is detrimental.

We know that mass can neither be changed nor be destroyed, but I want to know if there is any circumstance under which the mass of a body can be changed?

You are clearly not referring to relativistic phenomena or to pair annihilation and Einsteins' formula $E=mc^2$, as the other answers suggest, but to change of mass in massive bodies. In the first case rest mass is temporarily increased by energy, that in the case of speed is kynetic energy, in the case of heat is radiant energy, in the second case mass does not change, but is annihilated and transformed into EM radiation. I suppose you are referring to a massive body and not if mass is removed as when you are slimming.

You might be surprised to learn that no particular conditions are required for mass to change. In 1879 "The International Prototype Kilogram" was created (IPK, made of a platinum alloy known as Pt‑10I, which is 90% platinum and 10% iridium) and is kept in Paris. 40 copies of the IPK were made and were sent around the world and are kept by national metrology laboratories. (Cfr here) They were compared with the IPK in 1889, 1948, and 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK.

In this diagram and in this article you can see that, when all possible external reasons for mass-change have been accounted for, the masses of bodies (in this case: the standards) do change, in different parts of the world for unknown reasons:

What has become clear after the third periodic verification performed between 1988 and 1992 is that masses of the entire worldwide ensemble of prototypes have been slowly but inexorably diverging from each other. It is also clear that the mass of the IPK lost perhaps 50 µg over the last century, and possibly significantly more, in comparison to its official copies. The reason for this drift has eluded physicists who have dedicated their careers to the SI unit of mass. No plausible mechanism has been proposed to explain either a steady decrease in the mass of the IPK, or an increase in that of its replicas dispersed throughout the world

You may find more details in the quoted article