How can you compare the masses of two boxes without weighing them?

Question

How can you compare the masses of two boxes without weighing them?

Answer 1

Apply an equal force to both of them and compare the distances each travels. The mass of each box will be inversely proportional to t he distance traveled.

Answer 2

put them on a balance, one on each side, the heavier one will cause the balance to tip in it's direction.

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Answer 3

Stick them in water and measure the water dispersion?

Answer 4

Kick test them. Or if not too heavy, lift them.

Answer 5

Assuming little to no friction, one could simply push the boxes by hand and whichever one was harder to push would weigh more.  This is because mass, regardless of weight, still requires energy to move.  Even in a place like outer space, it would take more effort to push a more massive object than a less massive one.