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course phy 231
Lab activitiesNotes:
Include concise explanation: Whether specifically requested or not, all responses should include a brief explanation or description beginning on the line following other requested information. Abbreviations and incomplete grammar are acceptable; if you go too far with this I'll let you know, but I don't want to keep typing demands reasonable.
Reporting data:
· Data consists of what you observed, not what you concluded or how you got from observations to conclusions.
· Data should be presented in the specified format. If no format is specified, give a succinct data report in the form of a table.
· Unless otherwise specified, data should consist of numbers, with a subsequent note on the meanings and units of the numbers.
· Basic rule: Don't bury your data in a paragraph of explanation. It's OK if it appears that way within your explanation, as long as there's a succinct data summary.
Explaining your analysis:
· Typically the explanation of your analysis will include some combination of symbolic and numerical results in a sample calculation of one result.
· Other results should be reported in specified format; if no format is specified a list or a table would be appropriate.
1. Projecting point on CD onto paper on tabletop.
`qx001. Your points will lie along (or close to) an x axis perpendicular to the line you sketched on your paper. With the origin at the center point, what were the positions of your points corresponding to theta = 0, 30, 60, 90, 120, 150 and 180 degrees? Report as 7 numbers separated by commas in the first line, with brief explanation starting in the second line.
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5, 4, 2.5, 0, -2, -3.5, -5
I turned the CD rougly 30 degrees each time & the got the above numbers for the x distance in cm from the center of the CD.
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`qx002. What were the coordinates of your points corresponding to theta = 180, 210, 240, 270, 300, 330 and 360 degrees?
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-5, -4, -2.5, 0, 2.5, 4, 5
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`qx003. Suppose the disk rotated with a constant angular velocity, with an actual object moving along the tabletop just below the point on the disk. How would the velocity of that object change as the disk rotated through one complete revolution? Sketch (on your paper) and describe (below) a graph representing the velocity vs. clock time behavior of that point. Include an explanation connecting your results to your data.
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the graph makes a hill shape as the dot on the CD approaches the center. That is when the dot is moving the fastest in the x direction. Then as the dot goes to the left side it slows down in the x direction. So this would make the curve come back down just like on the first half but a mirror image.
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`qx004. For the same object as above, sketch a graph representing the acceleration vs. clock time behavior of that point. Desribe your graph and include an explanation connecting your results to your data.
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as the dot moves around the CD starting from theta=0, it speeds up until it reaches the center of the CD. So the beginning of this graph increases speed real fast so the point on the graph is up. Then it gradually slows down and levels out as it reaches the center of the CD. This looks like going down a hill on the graph paper. Then as the dot reaches theta =180 degrees, the dot slows down dramatically, appearing to stop, this makes the graph now go into the –y area of the graph, so the graph looks like on big hill that levels out at the top and bottom, with the steepest part going through y=0.
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`qx005. For the same object, sketch a graph representing the net force on the object vs. clock time for one revolution of the disk. Describe your graph and include an explanation connecting your description to your data.
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Net force is mass times acceleration, and since the above description is acceleration, and the mass is constant, that means that the graph will look similar to the acceleration graph except each y value will be increased by a factor of the mass. So the “hill” look will be taller and stretched out.
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... describe r, v and a vectors ...
2. Quick collision experiment
`qx006. In the first line below give the landing positions of the 'straight drop', uninterrupted steel ball, the marble, and the steel ball after it collides with the marble, separated by commas.
In the second line, report the horizontal displacement of the uninterrupted steel ball, the marble, and the steel ball after it collides with the marble, separated by commas.
Starting in the third line give the units of your measurements and a brief explanation.
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0, 8, 10, 6.5
8, 10, 6.5
cm. the marble( in my case, a tracking ball from a mouse because I redid this experiment at home and couldn’t find a marble) went further than the steel ball uninterrupted, and the steel ball fell real short after it struck the mouse track ball. Also, the height of my table was 70 cm.
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`qx007. Assuming that the time of fall was .4 seconds, what do you conclude was the velocity of each object at the instant it left the end of the last ramp? Report three numbers separated by commas in the first line, in the same order used in the preceding question. Units, explanation, etc. should start in the second line.
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176.5, 176.8, 175.7
cm/s, to get these velocities, for example, with the first number, I said It went 70cm down, and 8 cm out, so the root of those two numbers squared and summed is the distance, I then divided that number by .4 to get the velocity. I figured the velocity at the end of the ramp and the velocity when it hit the floor wouldn’t be too far off so I decided to calculate the average velocity. Since it was such a quick fall I figured that the acceleration of gravity wouldn’t affect the numbers that much so I negated them(especially since the acceleration of gravity wasn’t anything I observed in the experiment.)
At the end of the ramp the ball was not traveling in the downward direction, and its downward velocity is not constant. Its average speed when falling is as you give it, but that's almost all in the vertical direction.
The horizontal speed is just the horizontal distance divided by the time of fall.
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`qx008. In the collision, the velocity of the steel ball changed, as did the velocity of the marble. What was the change in the velocity of each? Report number in the first line, brief explanation in the second.
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.4 cm/s for both the steel ball and the mouse tracking ball.
I used the same method as I did before with finding the velocity with the NEW x distances. I took the velocity I got with this one and subtracted it from the old velocity and .4 was the change that I got for both.
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3. Motion of unbalanced vertical strap
`qx009. The original vertical strap system oscillated about an equilibrium position with one end lower than the other. Why do you think the equilibrium position had that end lower?
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because the center of mass was lower than the fulcrum. So when it would tilt, instead of coming back to the balance point, the imbalance cause the balance to stay where it leaned to.
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`qx010. What changed about the behavior of the system when a couple of #8 nuts were added to the higher end? What is your explanation?
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it helped to balance it. It seemed to oscillate in a more normal fashion and had a more linear response.
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`qx011. Would it have been possible to balance the system at a position where the end with the #8 nuts was higher? Would it have been challenging to do so? Explain.
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it would be challenging. The added weight to the one side made the system to want to have that end directly down, so it would have to be balanced perfectly to stay with the nut end up if possible at all.
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`qx012. Did the frequency of oscillation of the system appear to be constant?
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no. it would lean for a while to one side, and then ot the other side for a shorter period of time.
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4. Balancing the styrofoam rectangle
`qx013. Was the styrofoam rectangle easiest to balance when the paperclip was inserted along an axis through the point below its center of mass, at a point above its center of mass, or at the point of its center of mass? Why do you think it was so?
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below this created a non linear balance, but having the center of mass BELOW the pencil makes the system want to stabilize no matter what position it is in.
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`qx014. At which positions of the paperclip did the system did the system oscillate? At which positions did it appear to oscillate with constant frequency? At which positions did it appear to oscillate with nonconstant frequency?
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it oscillated when the clips were even with or below the pencil. It was most consistent the more the clips were in the middle. The system wouldn’t oscillate if the paper clips were above the pencil.
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5. Two cars with repelling magnets
`qx015. Why do you think the two cars traveled different distances when released?
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the cars had different masses and different frictional forces because of the weight difference.
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`qx016. Which car do you think exerted the greater force on the other?
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the one with the most mass exerted the higher force on the other
the force came from the magnets
When you hold the magnets close, does one magnet exert more force than the other?
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6. Graphs
`qx017. The graphs you were given in class depict coasting distance, in centimeters, vs. separation in centimeters, for a 120-gram toy car whose acceleration due to friction is 15 cm/s^2 (plus or minus an uncertainty of 10%). Sketch four tangent lines to the first curve, spaced equally from near one end of the curve and the other. Find, with reasonable accuracy, the coordinates of two points on each tangent line, and use these coordinates to find the approximate slope of each tangent line. In the first line below, report your four slopes. In the second line report the x and y coordinates of the two points used to find the slope of the third tangent line, reporting x and y coordinates of the first point then x and y coordinates of the second, using four numbers separated by commas.
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-2.3, -4.6, -.8, -.84
1.5,3.7, 4, 1.7
I didn’t have that paper that had the picture of the graph that you sent with us home, so I tried to improvise and use the similar looking graph in the 9-15 class notes.
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`qx018. Each centimeter of coasting distance corresponds to very roughly 2000 g cm^2 / s^2 of energy lost to friction. That energy came from the potential energy of the magnets at the given separation. So the vertical axis of your graph can be relabeled to represent the energy lost to friction, and hence the potential energy of the magnet system. For example, 20 cm on the vertical axis corresponds to 20 cm of coasting distance, each cm corresponds to 2000 g cm^2 / s^2 of potential energy, so the 20 cm coasting distance corresponds to 20 * 2000 g cm^2 / s^2 = 40 000 g cm^2 / s^2 of potential energy. The number 20 on the vertical axis can therefore be cross-labeled as 40 000 or 40 k, representing 40 000 g cm^2 / s^2 of PE. You should be able to quickly relabel the vertical axis of your graph.
Using the relabeled vertical coordinates, find the y coordinates of the two points you used to find the slope of your third tangent line, then report the x and y coordinates of those two points as four numbers in the first line below. In the second line report the rise and run between these points, and the slope. In the third line report the units of the rise, the units of the run and the resulting units of the slope. Starting in the fourth line explain what you think the rise means, what the run means, and what you think the slope means.
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1.5, 2.96K, 4, 13.6K
-6400 g cm^2/s^2
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`qx019. Report the slopes of all four of your tangent lines, in terms of your relabeled coordinates, as four numbers in the first line below. You can easily and quickly find these four slopes from the slopes you previously reported for the four tangent lines. Starting in the second line report very briefly how you found your slopes.
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-18400, -36667, -6400, -6750
In my rise and run of my slope. The number I got for the rise, I just multiplied that number by 8000 to match my renumbering of my graph.
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`qx020. University Physics Students: Find the derivative of the given y vs. x function y = 88 x^1.083 (this is a simple power function with a simple rule for its derivative) and evaluate at each of the four tangent points. Give the derivative function in the first line, in the second line the values you got at the four points, and in the third line compare your values to the slopes you obtained previously.
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y’=95.3x^(.083)
x=1.5,x=2,x=2.9,x=3.1
98.5, 101, 104, 105.
My slopes are not anywhere near the slopes I got form measuring because I didn’t use the right graph to go by. I understand that the derivative of a function tells you the instantaneous slope at that given point, and I know how I can use that too create a tangent line at that point with the slope that I found.
the function should have been y = 88 x^(-1.083); my error
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`qx021. University Physics Students: What is the specific function that describes PE vs. separation for the magnet system? What is the meaning of the derivative of this function?
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the function I got for my data with the car and magnet and proximity of the other magnet was y=.2x^2+21.
The derivative shows how much PE decreased by distance.
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Good work overall. See my notes.
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