Consider a ball suspended from the lid of a can using a string as shown in A1. A

Question

Consider a ball suspended from the lid of a can using a string as shown in A1. Another ball is attached to one end of a spring with the other end of the spring attached to the lid of a can, see B1. Think of the can as just a mass. The reason for using a can is simply that the lower rim of the can provides a convenient visual marker for any relative vertical movement of the ball.

A. For the ball and string case Suppose you hold the can at shoulder height and drop it. Which of the following would you expect? Make a guess and don

Explanation / Answer

Both cases are very similar, in one case we have a string attached to a ball and in the other case a spring. When the ball is dropped The free body diagram of both cases is similar. The weight points down and the tension force and the Spring force (kx) point up in each case respectively. It is important to notice that the ball and the can are uniformly accelerated at a rate of 9.8 m/s2. The experiment was conducted in both cases and the obtained results were:

In the string case (C) the string would go limp and the ball would move up relative to the can as in A2

In the spring case (C) the spring would return to it's equilibrium length as in B3

?This is due to the fact that both bodies (the can and the ball) are accelerated at the same rate so they would tend to collide with the ground at the same time, this means the position of the ball in both cases would tend to equilibrate with the can position. The air resistance would contribute to the equilibrium in positions.

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