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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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initial timing experiment
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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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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:
During this experiment I used our physics book, a plastic, empty cylinder jar, and a soft cover book about 1mm on a hard wood table. The object rolled in a straight line, and rolled at a constant speed.
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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:
&&&The first time the cylinder rolled before turning the book 180 degrees was: 3.875 seconds
The second was: 1.96875 seconds
When the book was turned 180 degrees it measured: 1.367188 seconds & 1.921875 seconds &&&
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Presumably you are giving time intervals in seconds, and if so the numbers you are giving make sense. This would be clearer if you included the units with the numbers (e.g., 1.367 seconds rather than the bare number 1.367).
In general if a quantity has units, the units should be included as part of the quantity. This helps you keep track of the meaning of the numbers, and greatly aids the general reader in understanding your information.
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&&&The cylinder picked up speed as it was moving down the incline, but during each trial the speed of the cylinder differed. &&&
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There is an important distinction between constant speed on the incline, which is clearly not the case here, and the same average speed on different trials.
The cylinder clearly doesn't roll at a constant speed, since it started with a speed of 0. Had the speed been constant, it would never have differed from 0, and the cylinder wouldn't have gone anywhere.
Clearly the cylinder starts from rest and picks up speed as it rolls down.
However your data indicate that the average speed of the cylinder differs from trial to trial.
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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:
&&&Before the book was turned 180 degrees the average roll was: 2.921875 seconds
And after: 1.6445315 seconds
&&&My measurements could be more accurate, but this was as close as I could get. My measurements were within at least .75 seconds of complete accuracy.
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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 cylinder started from rest (0) each time. The average speed would have been 2.58 seconds. &&&
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2.58 seconds is not a speed, it is a time interval.
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It isn't clear what 3.875 and 2.92 represent. These numbers are answers to the question of how fast the cylinder was moving, but they appear to be numbers you gave previously to questions about time intervals.
A time interval is definitely related to how fast something moves, but to get how fast you would have to divide the distance moved by the time interval.
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For the time intervals you measured, the cylinder always started from rest, with speed 0.
It will appear to have picked up speed as it rolled down the incline.
Using the time interval and distance you can find the average speed. So for each trial you will know the initial speed, which is 0 in each case, and the average speed.
The final speed is how fast the object is travelin at the end of the ramp. Since the initial speed is 0, the final speed will certainly exceed the initial speed.
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I do not believe that it was moving at a faster speed, because it wasn’t at a big enough incline. If it did, only .1 or .2 more at most.
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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:
&&&0 seconds, .67 seconds, 1.84 seconds, 2.15 seconds&&&
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You are giving time intervals or clock times where speeds were requested.
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My guess is that these are time intervals rather than speeds.
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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 followed the same experiment, same measurements, but used a bouncy ball instead. The ball is 1 inch round and wide, weighing about .5lbs. I calculated the ball with a timer on my phone. The first time I rolled the ball it was 2.1568 seconds, but the second time I rolled the ball it was 1.5960 seconds. The average was 1.8764 seconds. The ball did roll faster towards the end of the book. When turned 180 degrees the numbers were 1.236seconds and 1.151seconds, with an average of 1.1935 seconds.&&& I just added the units in here.
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You say that the ball rolled faster towards the end but you offer no evidence that it is so. To perform an experiment is to obtain and interpret evidence that indicates whether the hypothesis is or is not supported.
Your hypothesis will clearly be that the ball rolls faster toward the end. You need to obtain and interpret data to support (or reject) this hypothesis.
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I believe you have good data, but I'm going to ask you to revise a lot of your results.
You do need to include units with every quantity you report.
The question of 'how fast' is not answered by a time interval, but by a speed.
See my notes. I don't think you will have much trouble revising some of your results, but if you do please do ask questions, according to the instructions below:
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.
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Further revisions are needed, per my notes.
This time use #### before and after to indicate your insertions.
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