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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.
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7/14 noon
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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 am using our Physics book (Giancoli Physics Sixth Edition), the toy car I received in my lab packet, and the cover to my graphing calculator (About .5 inches in thickness) to prop up the book.
The toy car rolled very smoothly and in a straight line. Its speed increased as it crossed the book. The only thing that is not smooth is that the back wheels of the car catch on the side of the book so I have to make sure and start the car with the back wheels slightly in front of the side of the book.
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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:
Length of time it takes toy car to travel across book: 1.363 seconds
How far the car traveled: 22.7 cm
How much higher one end of the book is compared to the other: 0.9 cm
How far supports are from end of book: 25.6 cm
Reverse measurements:
Length of time it takes toy car to travel across book: 1.235 seconds
How far the car traveled: 22.4 cm
How much higher one end of the book is compared to the other: 1.1 cm
How far supports are from end of book: 25.4 cm
Time for the car to travel across from book was measured by hitting the timer button when I let go of the car and then hitting it again when the back end of the car dropped off of the book. I believe my times were pretty accurate because the timer measure the second out to the thousanths place and I got fairly consistent times when I timed it 3 times. The distance the car traveled was measured from the front tip of the car when the back wheels were slightly in front of the edge of the book to the other edge of the book. All my measurements with the ruler were very accurate and down to millimeters. How much higher the raised end of the book was was measured by resting the end of the ruler on the table with the numbers going up and measuring the space between the table and the edge of the book. The length between the supports and the end of the book was measured by starting at the edge of my calculator cover and measuring to the end of the book.
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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:
Average speed= 22.4 cm + 22.7 cm / 1.235 sec + 1.363 sec = 45.1 cm / 2.598 sec = 17.36 cm/sec
I think this speed is probably accurate to the tenths place. I determined this because the timer measures to the thousanths place but I could have been consistent in the time it took for me to hit the timer button, but I don’t think my reactions were slower than about 1/10 of a second.
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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:
Well I can’t determine how fast my object was moving at the beginning of the timed interval using my previous data. Of course the car was in place when the timer was started. But I would say that the car was moving slower than our average, which was 17.36 cm/sec, at the beginning of our timed interval because the car seemed to gain speed as it crossed the book.
But I will use the timer to figure out the average speed that the car was going during the first half of the decline. I will do this by figuring out how long it takes the car to travel 1/2 of the distance.
Average speed of first half= 10.5 cm / .765 seconds = 13.73 cm/sec
I believe that the object was probably moving at a speed greater than that of the average speed during the second part of the interval.
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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:
Final speed = 22.4 cm - 10.5cm / 1.235 sec - .765 sec = 25.31 cm/sec
Change in speed from beginning to end: 11.59 cm/sec
Initial Speed: 13.73 cm/sec
Average Speed: 17.36 cm/sec
Final Speed: 25.31 cm/sec
This means that the car gained speed as it traveled down the book. The initial speed was almost double the final speed and the average speed was in between the initial speed and final speed.
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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 am going to set up the car with the incline and measure how long it takes the car to fully cross the book and how long it takes for the car to halfway cross the book. I will take the halfway point’s distance and time to determine the speed for the first half of the trip. Then I will take the final distance and time and subtract the halfway point’s distance and time in order to find the speed of the second half of the trip. If everything is done correctly, then my speed for the second half should be greater than my speed for the first half.
Length of distance car will travel: 22.6 cm
Half way point: 11.3cm
Time for car to travel full distance: 1.523 sec
Time for car to travel to half way point: 0.993 sec
Speed of first half = 11.3 cm / 0.933 sec = 12.11 cm/sec
Speed of second half = 11.3 cm / 1.523 sec - 0.993 sec = 21.32 cm/ sec
My data shows that the speed of the car during the second half is 21.32 cm/sec and that the speed during the first half is 12.11 cm/sec. So these numbers prove that the car was going at a much faster speed during the second half of the trip in comparison to the first half of the trip.
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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?
1 hour & 15 minutes
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You may also include optional comments and/or questions.
I kinda did the final question while I was answering the previous questions. I now see that the previous questions were to be answered using speculation and then the final question is when you actually obtain solid number to prove your speculations.
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&#Very good data and responses. Let me know if you have questions. &#