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PHY 201
Your 'initial timing experiment' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Initial Timing Experiment_labelMessages **
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Note: The majority of student report taking less than an hour on this experiment, though a few report significantly longer times.
Take reasonable care to get good data in this experiment. Try to do the timing as accurately as possible. Measurements of length, height, etc. should be reasonably accurate (e.g., with a meter stick or ruler you can measure to withing +- 1 millimeter, but it's not necessary to try to determine fractions of a millimeter).
In this experiment you will use the TIMER program, a hardcover book, the toy car that came in your lab materials package (or, if you do not yet have the package, a cylinder or some other object that will roll along the book in a relatively straight line), and a ruler or the equivalent (if you don't have one, note the Rulers link, which is also given on the Assignments page).
• The book's cover should be straight and unbent.
• The toy car (or other object) should roll fairly smoothly.
Place the book on a flat level tabletop. You will prop one end of the book up a little bit, so that when it is released the object will roll without your assistance, gradually speeding up, from the propped-up end to the lower end. However don't prop the end up too much. It should take at least two seconds for the ball to roll down the length of the book when it is released from rest. For a typical book, a stack of two or three quarters placed under one end works well.
• Using the TIMER program determine how long it takes the ball to roll from one end of the ramp to the other, when released from rest. Once you've got the book set up, it takes only a few seconds to do a timing, so it won't take you long to time the object's motion at least three times.
• Determine how far the object travels as it rolls from its initial position (where you first click the timer) to its final position (where you click at the end of the interval). This will probably be a bit less than the length of the book, due to the length of the object itself.
• Determine how much higher one end of the book was than the other, and how far it is from the supports (e.g., the stack of quarters, or whatever you used to support one end) to the end of the book which rests on the table.
Then reverse the direction of the book on the tabletop, rotating the book an its supports (e.g., the stack of quarters) 180 degrees so that the ball will roll in exactly the opposite direction. Repeat your measurements.
In the box below describe your setup, being as specific as possible about the book used (title, ISBN) and the object being used (e.g., a can of vegetables (full or empty; should be specified) or a jar (again full or empty); anything round and smooth that will upon release roll fairly slowly down the incline), and what you used to prop the object up (be as specific as possible). Also describe how well the object rolled--did it roll smoothly, did it speed up and slow down, did it roll in a straight line or did its direction change somewhat?
your brief discussion/description/explanation:
I used the piece of wood supplied with the lab materials and two dominos to create the incline. I used the car supplied with the lab kit also. The length of the board was 301 mm long and the height was 20 mm. I drew lines on the board for the start stop of the time. The distance between the lines was the 301 mm length. The car rolled very smoothly and sped up as it went down the incline. It rolled in a pretty straight line.
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In the space indicated below report your data. State exactly what was measured, how it was measured, how accurately you believe it was measured and of course what the measurements were. Try to organize your report so the reader can easily scan your data and identify any patterns or trends.
your brief discussion/description/explanation:
I started the time at the top line and stopped it at the bottom line, which was at the top and the bottom of the board. The measurements, I believe, were fairly accurate. I am sure human error in starting and stopping the timer were likely the main reason the measurements were not the same. Of course, the accuracy of the timer is part of the factor as well but not a large percentage of this. My measurements are as follows.
First attempt Second attempt(reversed 180 degrees)
1.617188 1.640625
1.351563 1.726563
1.414063 1.632813
1.50 1.695313
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Using your data determine how fast the object was moving, on the average, as it rolled down the incline. Estimate how accurately you believe you were able to determine the object's average speed, and give the best reasons you can for your estimate of the accuracy.
your brief discussion/description/explanation:
The average time for the first attempt was 1.471 sec. The distance traveled was 301 mm. Ave. V = D/T = 301 / 1.471 = 204.62 mm/s = 204.6 mm/s
The aver time for the second attempt was 1.6738 sec. Same distance. Ave. V = 301/1.6738 = 179.83 mm/s = 179.8 mm/s
If you average all times together for both attempts you get an average time of 1.573. Ave. V = 301/1.573 = 191.35 mm/s.
I feel the second was likely more accurate because of the variance in the measurements. I feel that taking the average of four measurements helps to ensure that the accuracy is close to the actual time and speed.
The first attempt was 1.471 +/- 0.1461 and the second attempt was 1.6738 +/- .0528. As you can see, I must have gotten a lot better with my finger hitting the mouse as the variance is much smaller. The percent uncertainties using these averages and variances are 9.9 percent and 3.2 percent, respectively. I was about 300% less accurate the first time than the second time.
Averaging all attempts you get 1.573 +/- 0.2214 which gives you a percent uncertainty of 14.1 percent. This is why I feel that the four times for the second attempt are the most accurate.
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How fast was the object moving at the beginning of the timed interval?
According to your previous calculation, what was its average speed during this interval?
Do you think the object, when it reached the lower end of the book, was moving at a speed greater or less than the average speed you calculated?
your brief discussion/description/explanation:
At the beginning, the initial velocity was 0. The average velocities were 204.6 mm/s for the first attempt and 179.8 mm/s for the second attempt. If you average all times together for both attempts you get an average time of 1.573. Ave. V = 301/1.573 = 191.35 mm/s.
The car definitely appeared to be moving at a greater than average speed at the bottom of the board.
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List the following in order, from least to greatest. Indicate 'ties': The object's initial speed, its final speed, its average speed, and the change in its speed as it rolled from one end of the book to the other.
your brief discussion/description/explanation:
Initial speed = 0
Ave. speed
Final speed > ave. speed.
The car was constantly speeding up. Taking the average speed means there was greater speed and less speed than the average. Knowing that the speed was 0 at the top, you must have greater than average speed somewhere along the path and with constant acceleration, it would be at the end of the board.
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Devise and conduct an experiment to determine whether or not the object is speeding up as it rolls down the incline. If you have set the experiment up as indicated, it should seem pretty obvious that the object is in fact speeding up. But figure out a way to use actual measurements to support your belief.
Explain how you designed and conducted your experiment, give your data and explain how your data support your conclusions.
your brief discussion/description/explanation:
I did this two different ways. First, I drew a line exactly half way between the other two lines, a halfway point. I first timed the first half and the second half. Then I started the car at the half way line and let it roll to the bottom and got times for this interval.
First trial
First Half Second Half
0.84375 0.4140625
0.9921875 0.5078125
0.9453125 0.4921875
As you can see in this trial, the times are about half for the second half of the board as the first half of the board. This shows that the car was accelerating throughout and that the speed was greater at the bottom of the incline, the second half. Ave V of first half = 150.5mm/0.9271s =162.3 mm/s. Ave. V of the second half = 150.5 mm / 0.4714s = 319.3 mm/s. The velocity nearly doubled for the second half of the incline.
Second Trial
Time for second half of incline only-starting at halfway point
0.75
0.6875
0.8984375
0.8359375
Ave. V = 150.5 mm / 0.7930 s = 189.8 mm/s
This speed falls in between the different scenarios listed above for the average velocities for the entire incline so I feel this part of the experiment was inconclusive.
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Your instructor is trying to gauge the typical time spent by students on these experiments. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
Approximately how long did it take you to complete this experiment?
A little less than an hour.
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You may also include optional comments and/or questions.
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&#Very good data and responses. Let me know if you have questions. &#