If you have 2 iron spheres and a magnet, the lighter sphere will move first to the magnet. But with earths gravity fall tests we know that every object falls with the same speed when dropped no matter theirs weight. What makes it different?
In: Physics
This harks back to one of the most basic puzzles of physics.
Objects have two different ‘types’ of mass – there is gravitational mass, which changes how gravity affects an object, and there is inertial mass, which governs how the velocity of an object changes with an applied force.
There is, on the surface, no reason why they should be related, at all. As you say, they should be different like an object’s inertia and its magnetism are. But to the limit that we can measure them, they are identical.
It is this puzzle – why are these two types of mass seemingly identical? – that lead to Einsteins general relativity – he thought, if these two totally different things, inertial and gravitational mass, are the same value, might they actually be the same thing? That lead him to see gravity as a curvature in spacetime instead, and what we see as gravitational forces are in fact objects inertia as we force them to follow a curved spacetime.
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