The Newtonian Ant-Man problem!
Suppose somebody achieves the ability to become incredibly dense, or at least more than usual, by using the great space between the atoms of his body. Now this person, (regardless of whether it's possible or not let's assume it is just for the sake of the problem) is hitted by a train both in his dense and normal variations, in the dense one he has the volume of an ant and in the other one of a middle-age man. When does he gain a greater acceleration DUE TO THE TRAIN, who applies the same force in both cases? Assume they're rigid bodies meaning there's no force lost to the body being deformed, and ignore air resistance as you focus only on the force the train applies.
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5 solutions
The problem states the forces are the same in both cases, and the masses are the same, so by Newton’s 2nd Law we have F=ma which implies the same acceleration for both cases.
This is almost right if we consider only a rigid body, where forces are instantly communicated across the length of the object.
If we model the Antman and normal man as uniform blobs with different densities and different bulk moduli we will find that the speed of mechanical waves will be very different v = ρ B S . Thus, it isn’t hard to imagine that the force of impact will propagate almost instantaneously in the ant case, but in the normal size case would mean some parts of the body will feel the impact before the rest, likely leading to fractures etc.
Just a thought.