# A sealed ball is not connected to anything externally, but can have any complex mechanism inside. Can the mass change? [closed]

A sealed ball is not connected to anything externally, but can have any complex mechanism inside (mechanical, chemical, or any other). Can a wireless trigger from a remote or any other wireless mechanism make the ball's mass heavier? Take into account that the ball is sealed and therefore only internal changes can occur, no external objects should increase the mass.

PS: Someone suggested that the ball should create a Higgs field inside it which is impractical but theoretically correct.

## 1 Answer

Within the realms of practical engineering (the limits of this SE), No.

The Law of Conservation of Mass applies, and as such, if the ball is truly sealed, it cannot become heavier.

Even trying to cheat by using physics, No.

Mass-energy equivalence ($E=mc^2$) shows that an object that a bodies relativistic mass is greater than its rest-mass, that is to say, if a body is moving, it will be heavier than if the same body were stationary. Adding energy to an object adds mass, but, without approaching the speed of light (difficult, to say the least), you would struggle to measure the change.

But... The ball would have to be accelerated by an external energy source for this to work. Any mechanism inside the ball used to make it roll or spin (e.g. a motor) would require its own energy source, and, by the same equation shown above, a full battery weighs more than an empty battery.

Can I make the ball lighter, then? Yes, but you won't be able to measure it

If you allow the ball to radiate heat to it's surroundings, therefore, loosing energy, you could make the ball lighter (e.g. by running a heater off some batteries inside) without loosing any matter/atoms, but there is no way you could measure a change this small (see the excellent answer on the weight of batteries that I linked above for discussion on this).

One other thought: If an electromagnet were sealed inside, and the ball were near some iron filings, then the ball could pick up mass from the outside world, without breaking its seal, but, that seems like cheating your rules, rather than a solution.