Astronomy Ch04.9: Process of Science: Testing the Law of Gravity
Each diagram shows a single experimental trial in which you will drop a ball from some height. In each case, the ball’s size, mass, and height are labeled. Note that two diagrams show a basketball, one diagram shows a bowling ball of the same size but larger mass, and one diagram shows a much smaller marble with the same mass as the basketball. You have a timer that allows you to measure how long it takes the ball to fall to the ground. Which pair of trials will allow you to test the prediction that an object’s mass does not affect its rate of fall?
– mass:5.0kg ; size:bowling ball ; height:20m
– mass:5.0kg ; size:basketball ; height:20m
Assume you have completed the two trials chosen in Part A. Which of the following possible outcomes from the trials would support Newton’s theory of gravity? Neglect effects of air resistance.
– Both balls fall to the ground in the same amount of time.
Consider again the experimental trials from Part A. This time, you wish to test how the size of an object affects the rate of its fall. Which pair of trials should you compare?
– mass:0.5kg ; size:marble ; height:30m
– mass:0.5kg ; size:basketball ; height:30m
If you actually performed and compared the two trials chosen in Part C, you would find that, while the basketball and marble would hit the ground at almost the same time, it would not quite be exact: The basketball would take slightly longer to fall to the ground than the marble. Why?
– Because air resistance has a greater effect on the larger ball.
Einstein’s theory, like Newton’s, predicts that, in the absence of air resistance, all objects should fall at the same rate regardless of their masses. Consider the following hypothetical experimental results. Which one would indicate a failure of Einstein’s theory?
– Scientists dropping balls on the Moon find that balls of different mass fall at slightly different rates.