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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.
** Initial Timing Experiment_labelMessages **
9/3 1pm
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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:
For this experiment I used a large hard cover book entitled Merce Cunningham: Fifty Years by David Vaughn. ISBN 0-89381-624-8. The book is 313 mm long, 249 mm wide and 28 mm thick. It has a glossy cover jacket, which made for smooth rolling.
I did not have a toy car in my lab kit, so I used a Husky brand socket - hex head 7/16 inch. It was 46 mm long with an external diameter of 15mm. I propped the book up on one end on a stack of 3 quarters (2006, 1996 and a Bicentennial 1976) The stack of quarters was 5 mm high. The higher end of the incline was 5 mm higher than the lower end. Measuring from the bottom of the center of the stack of quarters to the lower end of the book we get 313 mm. I thought this would be slightly shorter given that the book forms the hypotenuse of the triangle but upon observation it is evident that the thickness of the book adjusts for this.
The socket rolled well. It rolled smoothly speeding up as it went but slowly enough for me to time when it reached the end of the book. It rolled in a generally straight direction with perhaps a very slight inclination to veer to the right.
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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:
Two things were measured.
1. The length of the book was measured to be 313 mm. Since the object was 15 mm in diameter, it was determined the the distance traveled in each trial was 298 mm. (313mm-15mm)
This was measured to within an accuracy of +/- 1 mm.
2. The second measurement was the time it took from when the object was released until the time it rolled off the end of the book. This was measured using the Timer.exe program. From previous experiments with this timer program, the accuracy is approximately +/- .015 seconds.
The results for the first five trials were:
3.070313 s
2.871094 s
2.933594 s
2.949219 s
2.996094 s
The second trial reversed the direction by 180 degrees. The results were
3.808594 s
3.683594 s
3.789063 s
3.839844 s
3.659313 s
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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:
First 5 trials
For the first set of 5 trials the average time was 2.962803 seconds. This was determined by adding up all the trials and dividing by 5 (14.81401/5 = 2.962803 seconds).
The distance remained constant at 298mm. So to determine average speed the distance was divided by average time of 2.962803 seconds. 298mm / 2.962803 seconds = 100.58 mm/s
Given that the trials varied by as much as .02 seconds, and that the average speed of the fastest trial was 101.58mm/s (298/2.933594) while the average speed of the slowest trial was 97.06mm/s ( 298mm/3.070313s), I think the average speed can be estimated to be accurate to within +/- 4.5 mm/s. (101.58mm/s - 97.06mm/s = 4.52 mm/s)
Second 5 trials
For the first set of 5 trials the average time was 3.756082 seconds. This was determined by adding up all the trials and dividing by 5 (18.78041/5 = 3.756082 seconds).
The distance remained constant at 298mm. So to determine average speed the distance was divided by average time of 3.756082 seconds. 298mm / 3.756082 seconds = 79.34 mm/s
Here the difference between trials was slightly smaller at .18 seconds. The average speed of the fastest trial was 81.44mm/s (298/3.659313) while the average speed of the slowest trial was 77.61mm/s ( 298mm/3.839844s), I think the average speed can be estimated to be accurate to within +/- 3.8 mm/s. (81.44mm/s-77.61mm/s = 3.83mm/s)
The second set of trials - after the direction was reversed, may have been slower due to some slight difference in the level of my floor where I conducted the experiment, which could have effectitvely made the course slightly steeper on the first set than the second set.
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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 of the timed interval, the object was moving at 0mm/s
Overall, the object moved at an average speed of 100.58 mm/s over the course of the interval.
I think the object was moving at a speed greater than the average spped when it reached the lower end of the book. To have started from 0mm/s, for some point in the interval it had to be travelling at less than the average speed. Therefore at the end it had to be travelling at 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:
Initial Speed
Average Speed
Final Speed (spied)
Change in Speed (tied)
Initial Speed is least because it is 0mm/s. Average speed is 100.58mm/s. Final Speed is some speed greater than the Average Speed based on the reasoning in the previous question. The Change in Speed is the Final Speed minus the Initial Speed. Since the initial speed is zero, the Change in Speed and Final Speed are equal.
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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:
To devise an experiment to determine whether of not the object is speeding up as it rolls down the incline, I decided to measure the time it takes to roll the first half the length of the book and compare that to the time it takes to roll the entire length. This experiment should provide evidence that the object is speeding up as it rolls and not instantly achieving average speed the moment it is released at the top of the incline.
I divided the length of the incline 298mm by 2 to get 149 mm as the mid point. I measured up from the bottom so as not to be confounded by the diameter of the object. Luckily the mid point was the tip of the nose of Merce Cunningham and thus made a distinct reference point for my experiment.
Since I jostled the book around in my set up, I decided to run another set of five trials for the full length.
I got the following times for the full lengths:
2.757813 s
2.777344 s
2.714844 s
2.683594 s
2.699219 s
The average time was 2.690163 s
The average speed was 298 mm/2.690163 or 110.77 mm/s
I then ran a set of 5 trials to the mid point and got the following 5 times:
2.074219 s
2.152344 s
2.167969 s
2.277344 s
2.292969 s
The average time was 2.192969 s
The average speed was 149mm/2.192969 or 67.94 mm/s
Based on the average speed over the full course we can see that the average speed in the first half of the course is considerably slower. Therefore we can say with near certainty that the object is increasing in speed as it rolls.
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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 and 45 minutes
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Excellent work.
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Task: `q006. Return to the 'Brief Assignments Page', take a quick look down the page, and describe what you see. It is recommended that you bookmark this page in your browser (e.g., add it to Favorites) so you can access it easily and quickly.
Be sure you locate and take a quick look at the instructions for completing assignments. You won't fully understand the instructions at this point, but be sure you see where they are.
There are probably additional things you don't understand right now about the Assignments page. You will get more specific and detailed information in subsequent Orientation assignments, and once you start actually using the page you will easily become accustomed to the routine.
Now return to your course homepage (which you bookmarked according to an instruction earlier in this document), and click on the link entitled 'Table of Assignments, Topics and Specific Objectives'. This page is a greatly expanded version of the 'Brief Assignments Page' which includes a great deal of detail on topics and specific objectives. For everyday use the Brief Assignments Page will suffice, but you may also find it useful to review content and objectives on the expanded version provided on the College Algebra homepage.
Briefly describe what you have seen:
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
For each assignment there is a list of problems that need to be done with a list of goals that the chapter wants accomplished and the specific details regarding the assignment.
Task: `q007. From the College Algebra homepage click on the link 'Course of Study'. Read it and acknowledge below that you have been able to find the syllabus and know how to locate it: Note that you should re-read the syllabus or course of study on or shortly after the first day of class, to be sure you have read the document that will apply to the term in which you are taking the course.
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
I have found and read the syllabus that talks about the class and what all it requires and what we are going to learn.
Task: `q008. Return to the your College Algebra homepage and once more click on link to the Brief Assignments Pages. Add this page to your bookmarks (e.g., in Internet Explorer, add to Favorites), and acknowledge in your response that you have done so.
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
I have bookmarked this page on my computer.
Task: `q009. On the College Algebra homepage, click on Link to Blackboard, and sign in using the same username and password you use to access the registration system. When the Blackboard screen comes up you should find at least one 'course' entitled 'Supervised Study ... ', where ... stands for the term (Fall, Spring or Summer) and year (e.g., 2012), as well as your College Algebra course.
Click on the Supervised Study ... site and give a brief description of what you see. You need not read all the information that appears, just take a quick look and give a line or two of description. (It is possible that you will be doing the Orientation prior to the beginning of the term, or shortly after registration; if so this Blackboard 'course' might not yet be available. You might also be doing this before your Blackboard enrollment is run. If either is the case, be sure to make a note to yourself to do check this page out on the first actual day of classes. You won't need it before then.).
Note that enrollment in Blackboard and enrollment in your course at VHCC are two separate things. Blackboard is 'unofficial' and always needs to be regarded as such.
Please respond with a statement detailing your understanding of the Blackboard Supervised Study 'course', and the unofficial nature of Blackboard.
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
I have looked at the blackboard page and supervised study for this course. They are there to look at our grades and get what ever we need for the class. For example the assignments that are due and it is a way for the insturctor to leave messages for us. On the site there are links to grades and a message about getting started.
Task: `q010. We might use various features of this Blackboard page, but the course is not delivered using Blackboard. Blackboard has a number of very good features, but it is of necessity a 'closed' system and not sufficiently flexible or efficient to be the primary vehicle. The one feature we are sure to be using is the Grade Center, where you can check your grades on tests and my comments.
At the Supervised Study ... site note the 'Check Grades' link. Your grades will be posted at the Supervised Study... site, not at the College Algebra site.
As explained in the opening message on both the Supervised Study ... and College Algebra sites, Blackboard is not likely to be used extensively in this course, except for posting grades.
Describe what you see at the Grade Center.
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
It is a list of everything that is due and right now the spots where the grades go are blank. Out to the right side of the blank areas is the total possible points we can get on each assignment.
Task: `q011. You need not look at any more of the Blackboard page, but you are welcome to do so if you choose, and you may ask any questions you wish in your response. If you have no questions, or do not feel the need to further explore this page, just respond with 'ok' or something of that nature.
**** Your response (insert your response beginning in the next line; the next line is blank and doesn't include the #$... prompt):
ok
@& Your responses need to be inserted into a complete copy of the part of the document you were instructed to copy. Nothing should be deleted from that copy. Your responses should be inserted in the specified manner.
I was able to review enough of this document to tell that you're doing OK, so I won't ask you to resubmit. However if you want the posted document to be complete, and/or if you want me to give it a more thorough review, you are welcome to insert your answers into a complete copy and resubmit. In any case, in future submissions be sure to include everything.*@