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course phy 231
9-12-10 5:00 pm
Here are some questions related to today's lab activities, and some things I want you to do using the materials you took home and the TIMER program. I have written fairly extensive class notes as well, but want to look over them before sending them tomorrow.Link to TIMER (worth bookmarking): Timer_b
Ball off ramp to floor
If you weren't in class to do this:
We measured the landing positions of the ball after rolling down three ramps, one supported by a domino lying flat on its side (least steep), one supported by the domino lying on its long edge and one supported by the domino lying on its short edge (steepest). You have some dominoes, a ball and a ramp so if you didn't get to do this at the beginning of class, you should be able to repeat this.
Everyone should submit the following:
Assuming that the ball fell to the floor in .4 seconds, after leaving the end of the ramp, and that after leaving the ramp its horizontal velocity remains constant:
How fast was it traveling in the horizontal direction when the domino was lying flat on its side?
21.4 cm/sec
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How fast was it traveling in the horizontal direction when the domino was lying on its long edge?
30 cm/sec
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How fast was it traveling in the horizontal direction when the domino was lying on its short edge?
37.5 cm/sec
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Pendulum count:
What was the length of the pendulum you counted, and how many counts did you get in 30 seconds?
7.5 cm, 45 swings in 30 seconds
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What therefore is the period of motion of that pendulum?
1.5 periods/second
that's the frequency, not the period
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How does your result compare with the formula given on the board, T = .2 sqrt(L) where T is period of oscillation in seconds and L the length in centimeters?
1/3 of my recorded time.
you didn't give the result of your substitution
it didn't take 1.5 seconds for each cycle
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How well did the freely oscillating pendulum synchronize with the bouncing pendulum of the same length? Which was 'quicker'?
3 to 1, bounce was quicker
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Ball drop
From what height did the drop of the ball synchronize with the second 'hit' of the pendulum, and what was the length of the pendulum?
87.5 cm, 7.5 cm
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How long should it have taken the pendulum between release and the second 'hit'? On what do you base this answer?
.4 seconds, position function 0=.875 -.5(9.81)t^2
9.81 is not a quantity based on anything observed in this experiment. However it does correctly tell you how long the ball would take to fall 87.5 cm from rest.
You observed the pendulum. Based on those observations, how long should it have taken between release and second 'hit'?
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Given you answer to the preceding, you know the time required for the ball to fall from rest to the floor, and you know how far it fell. What therefore was its acceleration?
5.4 cm/s^2
If the ball traveled 87.5 cm from rest during .4 seconds, its acceleration was much greater than 5.4 cm/s^2.
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Ball down long ramp
How would you design an experiment to measure the velocities v0, v_mid_x, v_mid_t and v_f for different values of v0?
Clock the times at the beginning, middle, and end of ramp..also find position after half time has passed and take positon/time to get v_mid_t. Vf is endpoint/time. v0
Good, but you don't say how you would observe the quantities.
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clock endpoints, start ball at different place but use same start point
How would you design an experiment to measure v0 and `dv for different values of v0?
Start ball before recording start point and clock how long it takes to get to start point and (take distance to start point)/(time to start point), then have that as v0
the calculation you give would give you an average velocity on the preceding interval; however v0 would be the final velocity on the preceding interval
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Rotating strap
For the strap rotating about the threaded rod, give your data indicating through how many degrees it rotated, how long it took and the average number of degrees per second. Report one trial per line, with a line containing three numbers, the number of degrees, the number of seconds, and the average number of degrees per second, separated by commas.
10 full in 8 seconds
13 full in 12 second.
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To do with the materials you took home:
Using the TIMER program with the materials you took home:
Bracket pendulum:
Shim the bracket pendulum until the 'strikes' appear to occur with a constant interval. Click when you release the bead, then click for alternate 'strikes' of the ball on the bracket pendulum (that is, click on release, on the second 'strike', on the fourth 'strike', etc., until the pendulum stops striking the bracket). Practice until you think you think your clicks are synchronized with the 'strikes'. Report the length of the pendulum in the first line, then in the second line report the corresponding time intervals below, separated by commas:
11.5 cm
.594,.625,.609,.594,.594
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Using the same length, set the pendulum so it swings freely back and forth. Click each time the bead passes through the equilibrium position. Continue until you have recorded 11 'clicks'. Report the corresponding time intervals below in one line, separated by commas.
.484,.719,.687,.719,.719,.625,.672,.658,.688,.671
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For both sets of trials, how do your results compare with the prediction of the formula T = .2 sqrt(L)?
.678. very close
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Ball down ramp:
Do your best to take measurements you can use to find vf, v_mid_x, v_mid_t and `dv using your ramp and ball, releasing the ball from rest. (You could use the TIMER to get decent data. If you wish you can use the fact that a ball falling off a typical table or countertop will reach the floor in about .4 seconds. Note: Don't let the ball fall on a tile or vinyl-covered floor. You don't want broken tile, and you don't want dents in your vinyl. You could put your book on a carpeted or otherwise protected floor and land the ball on the book.)
Briefly describe what you did and what your results were:
clicked on timer at beginning, middle, and end of ramp. Also counted 1,2,3,4,5,6,7,8,1,2 for total time, then redid trial and counted 1,2,3,4,5 and clicked the timer to get vmidt
V0=0 vmidx=.92 vf=1.33 'dv=1.33 vmidt=.75
You haven't reported your data, only your conclusions. They appear to be pretty consistent with what would be expected, so there's reason for optimism, but the results can't be validated without the data.
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Rotating strap:
Let the strap rotate on the threaded rod, as before. Click the TIMER at the start, and then at 180 degree and/or 360 degree intervals (the latter if it's moving too fast to do the former). Copy the output of the TIMER program below:
.828,.828,.891,1.0,1.187,1.34,1.828
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On the average through how many degrees per second was the strap rotating during each interval? Report in a single line, giving the numbers separated by commas. Starting in the second line explain how you did your calculations.
318 degress per second.
Added all clock times, divided by 7, then divided 360 by that answer
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The second column of the TIMER output shows the clock times. For a given interval the 'midpoint clock time' is the clock time in the middle of the interval. Report clock times at the beginning, middle and end of your first interval in the first line below. Do the same for your second interval, in the second line. Starting in the third line explain how you got your results.
33.813,34.227,34.641
34.641,35.055,35.469
took first clock time and added the second and then divided by 2 to get the mid clock time.
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"
This looks good overall. However see my notes.
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