#$&*
PHY 121
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energy conversion 1
#$&*
PHY 121
Your 'energy conversion 1' 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 that the data program is in a continual state of revision and should be downloaded
with every lab.
Most students report completion times between 2 and 3 hours, with some as short as 1
hour and some as long as 5 hours.
For part of this experiment you will use the calibrated rubber band you used in the
preceding experiment 'Force vs. Displacement 1', as well as the results you noted for
that experiment.
For this experiment you will need to use at least one rubber band in such a way as to
make it useless for subsequent experiments. DO NOT USE ONE OF YOUR CALIBRATED RUBBER
BANDS. Also note that you will use four of the thin rubber bands in a subsequent
experiment, so DO NOT USE THOSE RUBBER BANDS HERE.
If your kit has extra rubber bands in addition to these, you may use one of them.
You are going to use the rubber band to bind three of your dominoes into a block. If you
don't have extra rubber bands, you could use some of the thread that came with your kit,
but rubber bands are easier to use.
The idea of binding the dominoes is very simple. Just set one domino on a tabletop so
that it lies on one of its long edges. Then set another right next to it, so the faces
of the two dominoes (the flat sides with the dots) are touching. Set a third domino in
the same way, so you have a 'block' of three dominoes.
Bind the three dominoes together into a 'block' using a rubber band or several loops of
thread, wrapping horizontally around the middle of the 'block', oriented in such a way
that the block remains in contact with the table. The figure below shows three dominoes
bound in this manner, resting on a tabletop.
Now place a piece of paper flat on the table, and place the block on the paper, with the
block at one end of the paper.
Give the block a little push, hard enough that it slides about half the length of the
paper.
Give it a harder push, so that it slides about the length of the paper, but not quite.
Give it a push that's hard enough to send it past the other end of the paper.
You might need to slide the block a little further than the length of one sheet, so add
a second sheet of paper:
Place another piece of paper end-to-end with your first sheet.
Tuck the edge of one sheet slightly under the other, so that if the block slides across
the first sheet it can slide smoothly onto the second.
You are going to use a calibrated rubber band to accelerate the blocks and make them
slide across the table.
Tie two pieces of thread through to the rubber bands holding the blocks, at the two ends
of the block, so that if you wanted you could pull the block along with the threads. One
thread should be a couple feet long--long enough that if the block is at one edge of one
paper, the other end of the thread extends beyond the edge of the other paper. The other
thread needs to be only long enough that you can grasp it and pull the block back
against a small resistance.
At the free end of the longer thread, tie a hook made from a paper clip.
Use the rubber band you used in the preceding experiment (the 'first rubber band' from
your kit, the one for which you obtained the average force * distance results). Hook
that rubber band to the hook at the free end of the longer thread.
Make another hook, and put it through the other end of the rubber band loop, so that
when you pull on this hook the rubber band stretches slightly, the string becomes taut
and the block slides across the tabletop.
You will need something to which to attach the last hook:
Now place on the tabletop some object, heavy enough and of appropriate shape, so that
the last hook can in one way or another be fixed to that object, and the object is heavy
enough to remain in place if the rubber band is stretched within its limits. That is,
the object should be able so remain stationary if a few Newtons of force is applied.
Any rigid object weighing, or being weighted by, about 5-10 pounds ought to be
sufficient.
Your goal is to end up with a moderately massive object, to which the last hook is tied
or attached, with the rubber band extending from the hook to another hook, a thread from
that hook to the block (with a shorter thread trailing from the other end of the block)
With a slight tension in the system the block should be a few centimeters from the 'far'
edge of the paper which is furthest from the massive object.
If the block is pulled back a little ways (not so much that the rubber band exceeds its
maximum tolerated length) the rubber band will stretch but the last hook will remain in
place, and if the block is then released the rubber band will snap back and pull the
block across the tabletop until the rubber band goes slack and the block then coasts to
rest.
The figure below shows the block resting on the paper, with the thread running from a
hook to the rubber band at the far end, which is in turn hooked to the base of a
flatscreen monitor.
At the far end the rubber band is ready to be stretched between two hooks. A measuring
device is shown next to the rubber band; to get accurate measurements of rubber band
length it is recommended that a piece of paper be placed beneath the rubber band, and
two points carefully marked on the paper to indicate the positions of the ends. The
separation of the points can later be measured. Alternatively the two points can be
marked in advance at the desired separation and the system stretched accordingly.
Consult your previous results and determine the rubber band length required to support
the weight of two dominoes. Pulling by the shorter piece of thread (the 'tail' of
thread), pull the block back until the rubber band reaches this length, and on the paper
mark the position of the center of the block (there might well be a mark at the center
of the domino; if not, make one, being sure it is within 1 millimeter of the center, and
mark the paper according to this mark). Release the thread and see whether or not the
block moves. If it does, mark the position where it comes to rest as follows:
Make a mark on the paper where the center mark comes to rest by drawing a short line
segment, perhaps 3 mm long, starting from the center mark and running perpendicular to
the length of the block.
Make another mark about twice the length of the first, along the edge of the block
centered at the center mark.
This will result in a mark that looks something like the following, with the longer line
indicating the direction of the block and the two lines coming together at the center
mark: __|__. In the first figure below the lowest two marks represent the positions of
the center of the dominoes at initial point and at the pullback point. The mark next to
the domino is the horizontal part of a mark that looks something like |- ; the vertical
part of that mark is obscured by the blocks, and the mark it also tilted a bit to
coincide with the slightly rotated orientation of the block. In the second figure most
of the |- mark can be seen.
You will make a similar mark for the final position for each trial of the experiment,
and from these marks you will later be able to tell where the center mark ended up for
each trial, and the approximate orientation of the block at the end of each trial.
Based on this first mark, how far, in cm, did the block travel after being released, and
through approximately how many degrees did it rotate before coming to rest?
If the block didn't move, your answers to both of these questions will be 0.
Answer in comma-delimited format in the first line below. Give a brief explanation of
the meaning of your numbers starting in the second line.
Your answer (start in the next line):
1.2, 10
The domino block moved approximately 1.2 cm from the original position and twisted at
about 10 degrees.
#$&* _ 2 rb tension how far and thru what angle
Tape the paper to the tabletop, or otherwise ensure that it doesn't move during
subsequent trials.
Repeat the previous instruction until you have completed five trials with the rubber
band at same length as before.
Report your results in the same format as before, in 5 lines. Starting in the sixth
line give a brief description of the meaning of your numbers and how they were obtained:
Your answer (start in the next line):
.8, 5
.1, 0
1.4, 0
.1, 0
.4, 5
The first numbers are how far the domino block slid from the original position. There
was very little twisting with this set of trials, varying from 0 to 5 degrees.
#$&* _ trials on paper
Now, without making any marks, pull back a bit further and release.
Make sure the length of the rubber band doesn't exceed its original length by more than
30%, with within that restriction what rubber band length will cause the block to slide
a total of 5 cm, then 10 cm, then 15 cm.
You don't need to measure anything with great precision, and you don't need to record
more than one trial for each sliding distance, but for the trials you record:
The block should rotate as little as possible, through no more than about 30 degrees of
total rotation, and
it should slide the whole distance, without skipping or bouncing along.
You can adjust the position of the rubber band that holds the block together, the angle
at which you hold the 'tail', etc., to eliminate skipping and bouncing, and keep
rotation to a minimum.
Indicate in the first comma-delimited line the rubber band lengths that resulted in 5
cm, 10 cm and 15 cm slides. If some of these distances were not possible within the 30%
restriction on the stretch of the rubber band, indicate this in the second line.
Starting in the third line give a brief description of the meaning of these numbers.
Your answer (start in the next line):
8.4, 8.8, 9.1
These are the lengths of the rubber band for sliding the domino-block 5, 10, and 15 cm,
respectively. They were measured with an actual cm ruler, not the reduced ruler used
for the previous lab activity on calibrating the rubber bands. I did use that one,
however, for measuring the lengths for the Newtons.
#$&* _ rb lengths for 5, 10, 15 cm slides
Now record 5 trials, but this time with the rubber band tension equal to that observed
(in the preceding experiment) when supporting 4 dominoes. Mark and report only trials in
which the block rotated through less than 30 degrees, and in which the block remained in
sliding contact with the paper throughout.
Report your distance and rotation in the same format as before, in 5 lines. Briefly
describe what your results mean, starting in the sixth line:
Your answer (start in the next line):
1.7, 5
1.9, 5
2.9, 5
1.1, 0
2.2, 5
These were the results in cm of sliding the domino block using the tension previously
determined for supporting 4 dominos. I had some outliers here with the 1.1 and 2.9 cm.
#$&* _ 5 trials 4 domino length
Repeat with the rubber band tension equal to that observed when supporting 6 dominoes
and report in the same format below, with a brief description starting in the sixth
line:
Your answer (start in the next line):
2.2, 5
2.6, 5
2.9, 10
1.8, 5
3, 5
These were the results in cm of sliding the domino block using the tension previously
determined for supporting 6 dominos.
#$&* _ 5 trials for 6 domino length
Repeat with the rubber band tension equal to that observed when supporting 8 dominoes
and report in the same format below, including a brief description starting in the sixth
line:
Your answer (start in the next line):
1.9, 5
1.6, 5
3.1, 5
2.9, 5
2.7, 5
These were the results in cm of sliding the domino block using the tension previously
determined for supporting 8 dominos. The difference between the size of the rubber band
for 6 dominos and 8 dominos was only 1 reduced mm, so it was difficult to get accurate
results between the 6 and 8 domino trials.
#$&* _ 5 trials for 8 domino length
Repeat with the rubber band tension equal to that observed when supporting 10 dominoes
and report in the same format below, including your brief description as before:
Your answer (start in the next line):
5.4, 10
3.8, 10
2.7, 10
4.5, 10
5.4, 10
These were the results in cm of sliding the domino block using the tension previously
determined for supporting 10 dominos. The block started to twist more under the
increased pressure and I had to redo some of the attempts because the block twisted
about 90 degrees.
#$&* _ 5 trials for 10 domino length
In the preceding experiment you calculated the energy associated with each of the
stretches used in this experiment.
The question we wish to answer here is how that energy is related to the resulting
sliding distance.
For each set of 5 trials, find the mean and standard deviation of the 5 distances. You
may use the data analysis program or any other means you might prefer.
In the space below, report in five comma-delimited lines, one for each set of trials,
the length of the rubber band, the number of dominoes supported at this length, the mean
and the standard deviation of the sliding distance in cm, and the energy associated with
the stretch.
You might choose to report energy here in Joules, in ergs, in Newton * cm or in Newton *
mm. Any of these choices is acceptable.
Starting in the sixth line specify the units of your reported energy and a brief
description of how your results were obtained. Include your detailed calculations and
specific explanation for the third interval. Be sure to give a good description of how
you obtained the energy associated with each stretch:
Your answer (start in the next line):
10.7, 2, .56, .55, .2128 &&&& .1064 &&&&
11.5, 4, 1.96, .6618, 1.4896 &&&& .7448 &&&&
11.6, 6, 2.5, .5, 2.85 &&&& 1.425 &&&&
11.7, 8, 2.44, .6542, 3.7088 &&&& 1.8544 &&&&
12, 10, 4.26, 1.146, 8.094 &&&& 4.047 &&&&
I used Newton-centimeters for my units of energy. I multiplied the force in Newtons, as
determined from our previous lab activity, by the mean of the displacements of the
domino blocks to determine energy. So, for the first set, the mean of the displacement
was .56 cm. This corresponded to .38 Newtons of force. I multiplied .56 cm times .38
Newtons to get .2128 Newton-centimeters of energy.
@&
The .38 N force was the maximum for exerted by the rubber band, and was exerted only at the very first instant after release. That force decreased to 0 at the point where the rubber band went slack and did not persist through the entire time of the slide.
So it is not meaningful to multiply that force by the sliding distance.
It would be meaningful to average the .38 N and 0 N forces exerted by the rubber band at its initial and slack lengths, and multiply by the distance through which that average force occurred.
So your energies need to be revised.
*@
#$&* _ for each set of trials length, # dom, mean, std of sliding dist, energy _
describe how results obtained esp energy calculations
Sketch a graph of sliding distance vs. energy, as reported in the preceding space .
Fit the best possible straight line to your graph, and give in the first comma-delimited
line the slope and vertical intercept of your line.
In the second line specify the units of the slope and the vertical intercept.
Starting in the third line describe how closely your data points cluster about the line,
and whether the data points seem to indicate a straight-line relationship or whether
they appear to indicate some sort of curvature.
If curvature is indicated, describe whether the curvature appears to indicate upward
concavity (for this increasing graph, increasing at an increasing rate) or downward
concavity (for this increasing graph, increasing at a decreasing rate).
Your answer (start in the next line):
2.3, -.25
cm/Newton, -.25
The points had a good bit of scatter, but did not lend themselves to any kind of
sensible curve. For this reason, I made the graph linear. I used the first and last
points for my line. The other points were both above and below it and were about
equidistant from the best fit line that I drew.
#$&* _ sliding dist vs. energy slope, vert intercept of st line, how close to line,
describe curvature if any
Now repeat the entire procedure and analysis, but add a second rubber band to the
system, in series with the first.
For each trial, stretch until the first rubber band is at the length corresponding to
the specified number of dominoes, then measure the second rubber band and record this
length with your results.
When graphing mean sliding distance vs. energy, assume for now that the second rubber
band contributes an amount of energy equal to that of the first. You will therefore use
double the energy you did previously.
When you have completed the entire procedure report your results in the space es below,
as indicated:
Report in comma-delimited format the length of the first rubber band when supporting the
specified number of dominoes, and the length you measured in this experiment for second
band. You will have a pair of lengths corresponding to two dominoes, four dominoes, ...,
ten dominoes. Report in 5 lines:
Your answer (start in the next line):
11.2, 11
11.5, 11.6
11.6, 11.7
11.7, 11.8
12, 12.3
#$&* _ lengths of 1st and 2d rbs in series each of 5 trials
Report for each set of 5 trials your mean sliding distance and the corresponding
standard deviation; you did five sets of 5 trials so you will report five lines of data,
with two numbers in each line:
Your answer (start in the next line):
1.32, .3421
4.6, .6124
6.82, 1.645
13.82, 1.519
20.86, 2.602
#$&* _ sliding dist and std dev each tension
Give the information from your graph:
Give in the first comma-delimited line the slope and vertical intercept of your line.
In the second line specify the units of the slope and the vertical intercept.
Starting in the third line describe how closely your data points cluster about the line,
and whether the data points seem to indicate a straight-line relationship or whether
they appear to indicate some sort of curvature.
If curvature is indicated, describe whether the curvature appears to indicate upward
concavity (for this increasing graph, increasing at an increasing rate) or downward
concavity (for this increasing graph, increasing at a decreasing rate).
Your answer (start in the next line):
12.855, .8
cm/Newtons
The points made a line that sloped up gently, increasing at an increasting rate. The
points clustered well around the best-fit line without too many deviations.
#$&* _ slope, vert intercept, describe curvature
In the space below, report in the first line, in comma-delimited format, the sliding
distance with 1 rubber band under 2-domino tension, then the sliding distance with 2
rubber bands under the same 2-domino tension.
Then in the subsequent lines report the same information for 4-, 6-, 8- and 10-domino
tensions.
You will have five lines with two numbers in each line:
Your answer (start in the next line):
.56, 1.32
1.96, 4.6
2.5, 6.82
2.44. 13.82
4.36, 20.86
#$&* _ 5 lines comparing 1 rb to 2 rb trials
Your preceding answers constitute a table of 2-rubber-band sliding distances vs. 1-
rubber-band sliding distances.
Sketch a graph of this information, fit a straight line and determine its y-intercept,
its slope, and other characteristics as specified:
Give in the first comma-delimited line the slope and vertical intercept of your line.
In the second line specify the units of the slope and the vertical intercept.
Starting in the third line describe how closely your data points cluster about the line,
and whether the data points seem to indicate a straight-line relationship or whether
they appear to indicate some sort of curvature.
If curvature is indicated, describe whether the curvature appears to indicate upward
concavity (for this increasing graph, increasing at an increasing rate) or downward
concavity (for this increasing graph, increasing at a decreasing rate).
Your answer (start in the next line):
#$&* _ graph 2 rb dist vs 1 rb dist _ slope and intercept _ describe any curvature
To what extent do you believe this experiment supports the following hypotheses:
The sliding distance is directly proportional to the amount of energy required to
stretch the rubber band. If two rubber bands are used the sliding distance is determined
by the total amount of energy required to stretch them.
Your answer (start in the next line):
Overall, the experiment supports that the sliding distance is proportional to the amount
of energy required to stretch the rubber band. When using 2 rubber bands, the sliding
distance was significantly longer.
#$&* _to what extend is hypothesis of sliding dist prop stretching energy supported _ to
what extent for 2 rb
Your instructor is trying to gauge the typical time spent by students on these
experiments. Please answer the following question as accurately as you can,
understanding that your answer will be used only for the stated purpose and has no
bearing on your grades:
Approximately how long did it take you to complete this experiment?
Your answer (start in the next line):
2 hours
:
#$&*
*#&!
&#Your work looks good. Let me know if you have any questions. &#