#$&*
course phy201
9/16 915
120910Complete and submit the following documents in the same manner as previous documents.
qa_04
qa_05
query_02
query_03
Do the experiment Using the Timer Program. Most students report that this experiment takes less than an hour.
Questions related to today's class:
`q001. For your graphs of rubber band length vs. chain length:
Find chain lengths for four different representative lengths of rubber band 1.
****
(12.5 , 40) (17.2, 66.7) (19.2,76.7) (21.1 , 83.5)
#$&*
Find the lengths of rubber band 2 for those four chain lengths.
****
8.1cm ,13cm , 14.6 , 15.6
#$&*
Graph the lengths of rubber band 2 vs. the lengths of rubber band 1.
****
the second graphs slope increases at a slower rate,
#$&*
`q002. Reason out the answer to the following questions, based on the definition of average velocity as average rate of change of position with respect to clock time and average acceleration as average rate of change of velocity with respect to clock time, and the fact that for uniform acceleration the velocity vs. clock time graph is a straight line. Show explicitly and in detail how you are using the definitions and the graph.
A ball accelerates uniformly from rest, traveling 100 centimeters in 10 seconds. What are its final velocity and its acceleration?
****
fv is 20cm/sec acc is 10m/s^2
#$&*
@&
I believe the change in velocity is 20 cm/s, which would imply an acceleration of 2 cm/s^2.
*@
A ball accelerates uniformly, with its velocity decreasing from 20 cm/s to 10 cm/s as it travels 90 cm. How long does this take, and what is its acceleration?
****
takes 6 sec acc is -9m/s^2
#$&*
@&
What is the change in velocity?
How long does this change take?
What is the definition of average acceleration?
What therefore is the acceleration?
*@
A ball accelerates uniformly through a displacement of 60 centimeters, during which its average velocity is 20 cm/second and its final velocity is 30 cm/second. How long does it take and what is its acceleration?
****
Takes 3 sec acc is 20cm/sec^2
#$&*
@&
Time interval is correct.
What is the change in velocity? (It isn't -60 cm/s, which if true would lead to your result except for the - sign).
How long does this change take?
What is the definition of average acceleration?
What therefore is the acceleration?
*@
A ball accelerates from 10 cm/s to 30 cm/s, accelerating at a uniform 6 cm / s^2. How long does this take and how far does the ball travel?
****
30cm/s - 10cm/sec = DV of 20 cm/sec 20cm/sec / 6cm/s^2 = Takes 3 1/3 sec Travels 66 2/3 cm
#$&*
@&
Got it. Good.
*@
`q003. Give your data for the rotating strap, along with a brief explanation of how you obtained your data.
**** My pendulum had a ratio of 41 os/min, so I found that it equaled 1.46 sec/os and converted all recordings to seconds
degree of change change of time in seconds
1440 18.98
2498 27.01
380 7.3s
922 24.9
585 8.75
540 8.76
810 17.15
90 4.74
1440 25.55
2025 33.58
702 15.4
2135 33.58
#$&*
Find the average angular velocity of the strap for each trial.
****
75.86w/s
92.48w/s
52.05w/s
37.02w/s
66.85w/s
61.64w/s
47.23w/s
18.98w/s
56.36w/s
60.30w/s
45.58w/s
63.57w/s
#$&*
Find the angular acceleration of the strap for each trial, assuming that the angular acceleration is constant.
****
7.99w/s^2
6.85w/s^2
14.26w/s^2
2.97w/s^2
15.28w/s^2
14.07w/s^2
5.51w/s^2
8.01w/s^2
4.41w/s^2
3.59w/s^2
5.92w/s^2
3.79w/s^2
#$&*
Which appears to have the greater angular acceleration, the unloaded strap or the strap loaded with magnets? (University Physics students might not have observed the strap loaded with magnets).
****
According to my data the unloaded strip has a greater angular acceleration
#$&*
For the unloaded strap, construct a graph of angular acceleration vs. average angular velocity, and describe any trend of this graph.
****
My graph really doesn't have much of a trend to it, unless i did it wrong, my 6 points don't look like other graphs we have made.
#$&*
@&
You're probably saying that the points were all scattered to heck. That's what would be expected, since the acceleration is a result of friction, which is notoriously unreliable.
*@
`q004. Once more consider the domino on the balanced metal track. If you balance the system with the domino near the end of the track, you find that you can move it some distance without upsetting the equilibrium. If you then move the domino twice as close to center of the track and rebalance it, do you think you would be able to move the domino further without upsetting the equilibrium, or the same distance, or would a lesser distance suffice to upset the equilibrium?
****
It would take less distance to upset the equilibrium
#$&*
`q005. University Physics Students: Give your data for the angular displacement of the coasting strap vs. magnet proximity. Describe how your results were obtained.
****
#$&*
Sketch a graph of the angular displacement of the coasting strap vs. magnet proximity, and sketch a smooth curve that follows the trend you believe is indicated by your data.
****
#$&*
This assumption might or might not prove to be reasonable, but for the moment we will assume that the amount of energy required to rotate the strap through each degree is the same. So we can invent a unit we will call the degree_energy, which is the energy required to rotate the strap through one degree, in opposition to the frictional torque which opposes its motion. Our assumption is equivalent to the assumption that frictional torque for this system is constant, independent of the strap's position and angular velocity. With this assumption, each degree of rotation corresponds to one degree_energy, so that your graph can now be interpreted as a graph of energy vs. proximity.
Divide your graph into intervals, each interval corresponding to 1 centimeter of proximity, and find the slope for each of these intervals. For each interval list the slope and the midpoint of the interval:
****
#$&*
Sketch a graph of slope vs. midpoint, and describe your sketch:
****
#$&*
Explain why your last graph depicts rate of change of energy with respect to position vs. proximity.
****
#$&*
Explain why, since work is force * distance and energy is equivalent to work, this last graph therefore depicts the magnetic force vs. proximity.
`q006. University Physics Students: We could set up a rotating system similar to that used with the magnets, but relying on electrostatic forces, which might exert an inverse-square force of the form F = k / r^2, where r is the proximity of our two charges.
For the moment let's leave everything unitless and just look at the numerical implications of a force function F = 144 / r^2.
****
#$&*
How much force will be exerted at proximity r = 3, r = 6, r = 9 and r = 12?
****
#$&*
What is the approximate average force for the interval from r = 3 to r = 6? Answer also for the intervals between r = 6 and r = 9, and between r = 9 and r = 12.
****
#$&*
If the charges are brought to the r = 3 separation and released, then what would be the product of the approximate average force and displacement from r = 3 to r = 6? What would be the same result for the intervals between r = 6 and r = 9, and between r = 9 and r = 12?
****
#$&*
We could divide the interval from r = 3 to r = 12 into more than three subintervals. We could divide this interval into 10, or 100, or a million subintervals, and perform exactly the same type of analysis (though I wouldn't recommend it for the million-interval case). The approximation errors would pretty quickly become insignificant, so that with increasing numbers of subintervals our results would quickly approach a limiting value. What would this limiting value be?
****
#$&*
"
&#This looks good. See my notes. Let me know if you have any questions. &#