Somebody said they are different because of gravity.
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Weight is a result of gravity. If you are on earth, things with mass also have a specific weight because of Earth’s gravity pulling on them. But if you were on Jupiter, they’d have the same mass but a much higher weight (because Jupiter pulls more strongly than earth does). If you’re in freefall (e.g. orbit) in space there’s no apparent gravity, and objects seem to have no weight at all.
But, though all of this, the mass hasn’t changed! It’s an inherent property of the object. And mass has consequences other than weight. On earth we often conflate the effects of mass with the effects of gravity, but this is incorrect. We know that heavy objects are hard to move, but they’re actually hard to move for two reasons: one is that gravity creates friction with the ground, which creates drag. The other is that more massive objects require more energy to accelerate.
Imagine for a moment that you have a perfectly frictionless skating rink and two ten foot cubes, one made of lead and one made of styrofoam. If you push them on the frictionless surface, both will move (it’s frictionless, so any force will cause some velocity) but they won’t move at the same *speed*. A good hard shove will send the styrofoam rocketing across the floor, but the same shove on the lead brick will barely start it moving. Likewise, for slowing down. If you get the styrofoam block moving at 20 miles per hour and you get stuck between it and the wall, it’ll hurt a bit, but you won’t be seriously injured. If you do the same thing with the lead block, it’ll kill you. Again, we’ve taken out friction here, and thus the part of “hard to move” that’s caused by gravity. This is all a consequence of mass. Likewise, very massive objects are still hard to move in space, even though gravity isn’t a factor.
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