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course PHY 241
Draft instructions for collaborative lab. 3/8
Investigate the relationship between the angle of and incline and the acceleration of an object on the incline. I would like to set the experiment up with the following items.
Ball or toy car. The toy car would stay on track better but if it is cheap then we may have drag issues that will skew our results. A good quality toy car is preferable.
A ramp. Hardcover book or short board if it isn’t bowed in the middle. 1 to 2 foot ramp will allow for better timing. It may not be possible but if you were to have a Hot Wheels track section and a board this would be great.
Anything fairly thin (playing cards, coins, etc.) to prop up the ramp and change the slope. We need enough of whatever is used to make 3 different slopes. I think quarters may be the best.
Timer program.
Rulers. I prefer millimeters to measure both the height of the ramp and the length of the run.
Hypothesis: Steeper ramps will increase the acceleration. But by how much?
Step one:
First set up the ramp by placing your chosen ramp with one end propped up a small amount. Do a test run to see if your object will reach the end. If it does not you may need to raise the end a small amount more. Repeat until you achieve a smooth run.
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You also want the ramp to be steep enough to ensure a consistent start. If small imperfections in the wheels and/or the surface visibly delay some starts, they are also sufficient to speed up some starts, and the data will be subject to a coufounding level of uncertainty.
The hotwheels cars in the lab packages typically have coefficients of friction in the range of .02 - .03, meaning that a slope in the same range will be necessary for the car to travel along the ramp at constant velocity. An additional .02 or so, which can vary depending on the consistency of the surface, will often be enough to ensure a good start.
This has to be weighed against the fact that shorter time intervals are subject to greater uncertainties. So you don't want the slope to be too great.
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Step two:
Measure the height of the ramp. This is the rise. Write this down. Measure the length along the table (do not measure the sloped ramp. From the left to the right of the base. If this formed a triangle I would need the length of the base. Specifically I need from the bottom left corner of the board or book to the bottom right corner. This is the run. Write this down as well.
Step three:
Place the car or ball at the top of the ramp. Align it so that the back end or back tires (your choice) are aligned with the ramp. Measure from the front lip or edge of the ball to the end of the ramp. Right writethis down it will be needed to calculate our information. This is our displacement.
Step four:
Place the car or ball at the top of the ramp. Align it so that the back end or back tires (your choice) are aligned with the ramp. This ensures the same distance every time. Release the car and click to start the timer at as close to the same moment as possible. When the front lip of the car reaches the edge of the ramp click the timer again. * Again right this information down. Repeat 3 times for this angle.
*This may be possible depending on your equipment. If you can do a few test runs and predict where the car or ball will reach the end of the ramp you can align your mouse pointer with the timer button the align the mouse itself with the button where the car will impact. When the car reaches this point it will automatically click the button for you. Just don’t forget to click the mouse button when you start. This is entirely optional. But It would reduce the “human error” of timing the click correctly. If you don’t like it just do the experiment normally.
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Good idea, provided the car has sufficient momentum to click the mouse being used. It's plausible that it could.
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Step 5:
Repeat steps 2,3,and 4 for a slightly higher ramp (try for double the height(if using quarters 1 for the first ramp 2 for the second ramp)). Note that the base length will have changed and need to be measured again.
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The 1-quarter increase might or might not be enough to result in a clear difference in the timing. If not, an increment of 2 quarters, or even more, might be preferable. However too many quarters would result in times too short to measure accurately, so again different factors need to be balanced.
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Step 6:
Repeat steps 2,3,and 4 for a slightly higher ramp (try for triple the height of initial ramp(if using quarters 1 for the first ramp 3 for the third ramp)). Note that the base length will have changed and need to be measured again.
Step 7:
After you have all data put it in a useful format. I like excel spreadsheets. We can export it into comma delimited format for the final report and it will be easier for us to manage.
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If the experimentalist has Excel this is a good idea. If not, a comma-delimited text file can be imported into Excel.
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Any questions can be sent to lester.caleb@gmail.com
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This address is OK since this communication is between the two of you.
However your experimentalist should also have the option to use the email function associated with your group at the Blackboard Supervised Study 2013 site.
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Your instructions look very good, but see my notes for a couple of things to think about.
Having made any edits you deem appropriate you can send the instructions on to your experimentalist.
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