| Physics for the Inquiring Mind [Phys 105] Fall 2003 |
[1] As a group, go to one of the five tracks in the room. Open Lab109P2.
[2] Last time, you found that the ball was traveling at a constant speed on the horizontal portion of the track (as evidenced by the fact that a position vs. time graph was a straight line). You also found (obviously) that releasing the ball from a greater height increased its speed on the horizontal portion of the track.
[3] Now suppose that someone makes the statement "If you double the height from which a ball is released on a track, it will double the speed with which it rolls on the horizontal portion at the bottom of the track". You are going to use your aluminum ball (the lighter one) to test this statement, as outlined below.
When testing this statement, your "height" should be the difference between the ball's height at the release point and its height on the horizontal portion of the track.
[4] Release the aluminum ball from a height of 7 cm and determine its speed on the horizontal portion of the track. After you have done this, double the height to 14 cm, and measure the ball's speed on the horizontal portion of the track again.
[5] So, is the statement that you are testing true? If not, was the ball's speed on the horizontal portion of the track more or less than that predicted by the statement?
[6] By experimenting with different release heights, determine the release height necessary to make the aluminum ball go twice as fast as it did when released from 7 cm.
[7] What is the ratio of these two release heights?
[8] If released from the same height, do you think that the speed of the brass ball will be greater, less than, or equal to the speed of the aluminum ball? Test your prediction.
[9] On the first day of class, you took a diagnostic test that included the following question:
Two metal balls are the same size, but one weighs twice as much as the other. The two metal balls roll off of a horizontal table with the same speed. In this situation
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both balls hit the floor at approximately the same horizontal distance from the base of the table. |
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the heavier ball hits the floor about half as far horizontally from the base of the table as does the lighter ball. |
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the lighter ball hits the floor about half as far horizontally from the base of the table as does the heavier ball. |
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the heavier ball hits the floor considerably closer to the base of the table than the lighter ball, but not necessarily at half the horizontal distance. |
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the lighter ball hits the floor considerably closer to the base of the table than the heavier ball, but not necessarily at half he horizontal distance. |
In case you're interested, your class answered the question in the following way:
Choice A: 6 Students
Choice B: 4 Students
Choice C: 2 Student
Choice D: 11 Students
Choice E: 1 Students
Set up a quick experiment to test which of the above choices is true. In so doing, compare the behavior of your aluminum and brass balls. They are the same size, but the brass ball has approximately 3.5 times as much mass as the aluminum ball. Note that you will have to flip the horizontal portion of your track so that the balls are free to fly off of the table.
Was the majority correct? If not, which is the best answer?
[10] The following Homework will not be due until Tuesday, November 18, but I am including it here in case you want to get a head start on it: Exercise 6.5 on p. 674.