How are mass, weight, and gravity measured in space? Are these measurements just hypotheses or can we conclude with certainty on them?
In: Physics
“Weight” is just a word meaning “force due to gravity.” If there is no gravity, there is no weight.
“Mass” is a property of the actual object in question, regardless of whether or not there is gravity. You can measure mass indirectly, but not using a scale (since scales measure *weight* and there is virtually no weight in almost-0 gravity).
You could measure mass using any other quantity that depends on mass, i.e. a quantity which you actually *can* measure. For example, momentum. If you throw a 5-kg object at your fellow astronaut and they catch it, you can measure their resulting speed (since they will be thrown backward when they catch the object) and that will indirectly tell you what your fellow astronaut’s mass is because of conservation of momentum.
So if you can think of some other (measurable) quantity that depends on mass you can indirectly calculate the mass by measuring that quantity.
Well mass is easy, that’s just density x volume, which are essentially constant. Weight is just a function of mass x gravity and gravity is a constant determined by the size of the relevant planet or celestial body.
In space gravity is negligible, usually refered to as microgravity, but isn’t zero.
Mass is pretty much how much energy that thing has. When you measure the mass of something, you’re measuring the potential energy it has. Of course, that means mass can include kinetic energy. So, faster objects have (slightly) bigger mass.
Since we know the relationship between mass and other properties (like force and acceleration), we can calculate (=measure) it’s mass.
I’m going to guess that there’s no way to measure the energy something has directly but I might be wrong.
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