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Phy 121
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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I apologize for the assignments being turned it at the last minute. I didn't get my book until the weekend through the mail, then I just received my lad kit today. I hate turning things in like this. I'm sorry. Just wanted to let you know!
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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 the Physics book by Giancoli (01306060200) to complete this experiment. The object I am rolling is the toy car that came in my lab kit. I have my book propped up on the bottom, underneath the title of the book. The book is propped up using the spiral side of the 1 subject notebook which would be equivalent to three quarters stacked on top of each other. The car rolled smoothly, but at times the wheels would lock up for a split second. It only did that on one roll (first roll). The car seemed to spend up a little bit as it got closer to the end of the book. The car rolled straight ahead with no direction change.
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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:
First Roll: 1.6 seconds using the timer; traveled 22.86 cm (+- 2 cm/ +- .2 seconds) on the book (measured by ruler).
Second Roll: 1.74 seconds; traveled 22.86 cm (+-2 cm / +- .2 seconds)
Third Roll: 1.24 seconds; traveled 22.86 cm (+- 2 cm / +- .2 seconds)
Rotated 180 degrees
First roll: 1.08 seconds; 22.86 cm (+-2 cm/ +- .2 seconds)
Second Roll: 1.04 seconds; 22.86 cm (+-2 cm/ +- .2 seconds)
Third Roll: 0.94 seconds; 22.86 cm (+-2 cm/ +- .2 seconds)
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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:
Well, first I would add all 6 times and then divide by 6 to receive the average. The average speed was 1.78 seconds. I believe that I determined the average speed pretty close, but definitely not exact. I dont know if it is exact because there could have been a delay in me releasing the car and hitting the button. I feel that there was definitely a delay between the two.
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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: The car was moving 1.6 seconds down the slope in the beginning of the timed interval. During the first three rolls, the average speed was 1.33 seconds. I believe that the car would be speeding up by the end of the book, because at the beginning (after releasing) it is building up speed down the incline. So it should be still speeding up until it falls off the book. It would be speeding up greater than the average speed.
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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:
1.6 seconds / 0.94 seconds / 1.78 / 0.66
The 1.6 seconds is the very first run I did. The 0.94 was the very last run I did. The 1.78 is the average of all the data. 0.66 is the 1.6 - .94
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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:
Set up the book and car as previously stated. Use the timer to time how long it take the car to get to the half way point on the book. Then time how long it takes for it to go from the half way point to the end. I used a pen to mark the half way point.
It took the car 1.16 seconds to reach the half way mark. Then it took the car .5 seconds from the half way mark to the end of the book which proves that it is speeding up in the second half of the run.
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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?
It took approximately 45 minutes to complete this assignment.
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You may also include optional comments and/or questions.
I felt like I did okay on the experiment, but I had a hard time deciding if I was completing these problems correctly:
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.
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?
I understand about taking the average, but I believe it was the wording in the questions that threw me such as: initial speed (does that mean the beginning time? The first run?), final speed (the last run?) , beginning of the timed interval (first run?), what was its average speed during this interval? (the average of the three runs before we rotated the book?)
@& A timed interval starts with one click and ends with another. The initial speed is how fast the object is moving at the instant of the first click (if the object is released from rest on the first click that would make the initial velocity zero) and the final speed is how fast it is moving at the instant of the second click. (Velocity is like speed except that it has a direction.)
We would typically expect the average velocity to be between the initial and final velocity, though if the object is speeding up and slowing down during different parts of the interval this might not be the case.*@
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&#Good work on this lab exercise. See my notes and let me know if you have questions.
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