Say you have a sandbox you play in, in your backyard.
Mass: How much sand is in the sandbox, doesn’t matter if you’re in space or on the moon it doesn’t change the actual quantity of sand
Weight: How heavy that sandbox is to lift if you want to move it. Weight will decrease on the moon, or increase on the surface of the sun.
Density: How much space the sand occupies. You could melt the sand, and it would take up less space making it more dense
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