Final answer:
When two balls, one twice as heavy as the other, are released from the same height in a vacuum, they will hit the ground at the same time due to the constant acceleration of gravity. The equivalence principle confirms that all objects fall at the same rate when air resistance is absent. The mass of the objects does not affect the rate of fall in such conditions.
Step-by-step explanation:
When you release two smooth balls from the same height, one twice as heavy as the other, they will both hit the ground at the same time if air resistance is negligible. This is because the force of gravity accelerates all objects at the same rate, regardless of their mass. Galileo's experiments, as well as the concept of the equivalence principle proposed by Einstein, support this outcome. If heavy objects fell faster than lighter ones, it would indeed violate this principle. Experiments such as dropping a book and a crumpled paper ball from the same height demonstrate that when air resistance is not a factor, objects fall at the same rate.
In addition to this, if you perform an experiment with two balls of different masses, like a tennis ball and a basketball, different interactions will occur depending on their relative positions when dropped. Dropping them side by side will result in them hitting the ground simultaneously, but dropping the tennis ball above the basketball can lead to an interesting exchange of momentum, causing the tennis ball to bounce higher due to the transfer of energy from the basketball's bounce.