Question

When a liquid evaporates inside a cup,what happens to its mass and weight ?

Answer 1

Answer:

Mass is conserved, as your other answers note. Nothing you can do, short of relativistic speeds, will change the mass.

The weight - well, weight is a force that is dependent on the two masses involved (in fact, all masses involved, but we will limit ourselves to the ideal two here) and the distance separating them, so there is lots of room for change here. Also, you can get tricky and orbit the larger mass and lower your effective weight to micro-values. However, if we limit ourselves to a single place on Earth’s surface when the liquid evaporates it still has the same weight it had as a liquid, but its density is a lot less. Also, as it disperses into the atmosphere and its density is lowered while its volume increases, it gets to some extent buoyed up by the atmosphere. Heavy vapors tend to sink in the atmosphere and lighter ones rise, but a little turbulence (like solar warming if the surface) will mix the gasses, countering the effect, and allow the evaporate to disperse further.

So mass is constant under all non-relativistic actions, and weight is constant if we limit the action to the surface (or some fixed elevation above it) of the planet creating the weight.

I hope this will help you