course Phy 122
Question: This question, related to the use of the TIMER program in an experimental situation, is posed in terms of a familiar first-semester system.
Suppose you use a computer timer to time a steel ball 1 inch in diameter rolling down a straight wooden incline about 50 cm long. If the computer timer indicates that on five trials the times of an object down an incline are 2.42sec, 2.56 sec, 2.38 sec, 2.47 sec and 2.31 sec, then to what extent do you think the discrepancies could be explained by each of the following:
The lack of precision of the TIMER program.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
I think the extent that the precision is the reason for the discrepancies is small. I feel the Timer program is pretty precise.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Pretty great extent. Human error is always a factor in the lab setting. If someone has a slow reaction time, the numbers can drastically be changed.
Actual differences in the time required for the object to travel the same distance.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Very little extent.
Differences in positioning the object prior to release.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
This plays a huge part in the differences in times.
Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think the discrepancies are explained by this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Very big part in the discrepancies. Like I stated before, human error is so common.
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Question: How much uncertainty do you think each of the following would actually contribute to the uncertainty in timing a number of trials for the ball-down-an-incline lab?
The lack of precision of the TIMER program.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I think the TIMER program is very precise, so I think there is very little uncertainty.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I think this factor would greatly contribute to the uncertainty. Human error is different with every person; not everyone has quick fine motor reflexes.
Actual differences in the time required for the object to travel the same distance.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv I think this factor would contribute very little to the uncertainty
Differences in positioning the object prior to release.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv This would contribute greatly because the different points of release would affect the times.
Human uncertainty in observing exactly when the object reached the end of the incline.
To what extent to you think this factor would contribute to the uncertainty?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv Again, human fine motor skills are different and would greatly affect the uncertainty.
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Question: What, if anything, could you do about the uncertainty due to each of the following? Address each specifically.
The lack of precision of the TIMER program.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv Find a different program that was programmed to be more precise.
The uncertain precision of human triggering (uncertainty associated with an actual human finger on a computer mouse)
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv Use the same human for all the tests as to ensure that the same uncertainties in human triggering is atleast consistent.
Actual differences in the time required for the object to travel the same distance.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv We could change the amount of friction of the surface to ensure that friction is not a part of the uncertainty.
Differences in positioning the object prior to release.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv We could make a clear line that every object has to be released at.
Human uncertainty in observing exactly when the object reached the end of the incline.
What do you think you could do about the uncertainty due to this factor?
your answer: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv We could use a photographic system to check it right when it reaches the end. Or we could use the laser light timers that I have previously used in a Physics class that uses gates and a laser beam to check when something crosses it path; it will time once it starts or stops.
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Great comments, especially at the end. You demonstrate a lot of insight.
Gates and laser beam work very well as long as the first and last point detected accurately indicate the relative positions of the object. However if you don't keep things precise right angles, unexpected errors creep in. The accuracy of the instrumentation can mislead one as to the accuracy of the experimental setup. Spherical objects, for example, can be tricky to time using photogates (though care in the setup can minimize error).
A photographic system requires a means of accurately indicating the time. An accurate stroboscope can be very useful, and if care is taken with the electronics of that device the results can be excellent. A mechanical clock with a uniformly rotating second hand, or a hand rotating at a smaller fraction of a second, can also be very useful.
The errors in these systems can be subtle, which is why I like to use pendulums during the early part of the class.
The most accurate measurements I've been able to achieve in the lab have been with sound editors (capture the waveform of sounds produced at release and at the end of the thing being timed). It takes a very expensive stroboscope or photographic system to beat that. However if we want to time more than one event per interval, the production of sounds requires energy which interferes with the motion we're trying to time.
As you'll see later, it's easy (using a little carbon paper) to measure the beginning and ending positions of a spherical projectile with excellent precision, and if you can control and measure the initial angle, you can determine the initial velocity quite accurately with a simple setup.
&#Your work looks good. See my notes. Let me know if you have any questions. &#