ball down incline (from Class Notes 100823)

You can calibrate a fast, but not forced, 10-count by repeating the count 10 times and seeing how many seconds are required.  If you have a reasonably good sense of pace, this gives you a reasonably accurate timing device.

We timed a ball as it rolled approximately 30 cm down a ramp.

When the ramp was level, the upward force exerted on the ball by the ramp was equal and opposite to the downward force of gravity and the ball did not move.

When one end of the ramp was supported by a thick washer most of the class obtained times between 2 and 3 seconds.

The following questions were posed:

• How fast was the ball moving?
• Did its speed change?  If so, how do you answer the question of how fast it was moving?
• Clearly the speed changed.  The question then is 'how quickly did the speed change'?
• You need to give these questions some thought before the next class.

You also observed the system when the ramp was supported by two washers.  The same questions apply.

An additional question:

• Based on your results, with what certainty can you conclude that the ball's average velocity was greater when the ramp was supported by two washers?
• Based on your results, with what certainty can you conclude that the ball's speed changed more quickly when the ramp was supported by two washers?

You observed the system when one end of the ramp was supported by two washers, and the other by a single thickness of paper. 

• If the average observed time was greater for this system than for the two-washer system without the paper, would this constitute evidence that the paper made a difference?
• If the average observed time was less for this system than for the two-washer system without the paper, would this constitute evidence that the paper made a difference?
• How could the number of trials affect your conclusions?
• If we replaced the paper by a washer half as thick as the ones at the other end, would you be able to distinguish its presence based on your observations?
• What if the washer was only half that thick?
• What if the washer was only half as thick as that?
• Just how thin could that washer get before you would be unable to distinguish its effect by timing the ball down the ramp?

Now do the following:

• Find whatever information you can about the ball's speed on the one-washer ramp.
• Find whatever information you can about the ball's speed on the two-washer ramp.
• Make your best effort to figure out how quickly the speed changed on each ramp.
• Organize your data and your analysis in such a way that you can always refer back to it later and understand what you did in the experiment, and in the analysis.