Sliding Friction Lab
50 points
Procedure I:
1. Plug a Force Probe into channel 1 of the Logger Pro box and set it for +/- 10N
2. Open Logger Pro on the computer. You must plug in the device BEFORE opening Logger Pro on the computer so it will recognize the equipment. Click on the y-axis numbers and MANUAL set it for -1N to 10N. Click on the x-axis and MANUAL set it for 0 to 20 seconds.
3. Set up a ramp as illustrated in the diagram below: The ramp should be tilted so that if the mass were released, it would slide down the ramp. (In physics mumbo-jumbo: You should set angle q such that it exceeds mstaticfriction). Measure angle q because we are going to use Physics formulas later to solve for it. We want to see how close we were. Record your Measured Angle q in the data table below.
4. Hold the Force Meter so that it is straight on to the mass (as shown in the above diagram).
5. Holding very still, hit the collect button on the computer and collect the Fhill on that mass (you’ll know how still you’re holding when you look at the line on the graph).
6. Use the mouse arrow to highlight at least 100 data points and then hit CTRL-C on the computer to copy those data points onto the computer’s clipboard. We are NOT interested in the TIME, just the Force (N). (You might have to copy both - the computer might not let you just copy just the one column. But, when you paste it into Excel, you can just ignore the Time data)
7. Open Excel.
8. Paste the 100 Force (N) data points into Excel and find their average. (In Excel, click on an open field box and write the following: =average(a1:ax) (Where “a” is the column name and “x” is the last number in the row series) Record Average Fhill on your data table below.
9. Return to Logger Pro (the program that runs the Force detector) and click on the DATA bar and select “store latest run”.
10. Change the angle q of your ramp. Go to a steeper angle. Repeat Steps 4-9.
11. Change the angle q one last time and repeat steps 4-9.
Procedure II
1. Hold the mass on the ramp at some angle greater than mstaticfriction . Hit the collect button and hold steady for about 3 seconds. Then, begin to pull it up the ramp and hold your speed constant at some maximum speed (in other words, you will need to accelerate from 0 m/s to some x m/s).
Answer these questions (type your answers in red and write them right next to the questions here!)
a. What was the average force on the mass when you were holding still for those 3 seconds? __________
b. What happened to the graph when you accelerated from 0 m/s to your x m/s? Did it a) Jump up? b) Stay the same or c) jump down? No numbers here, just answer qualitatively
c. What was the maximum value of force reached upon your acceleration? (I want a numerical value here)
d. What happened after you reached your x m/s speed? Did the force line continue to climb? Did it hold steady? If it held steady, was the value greater, less than or equal to the value when you were just holding the block still (question a).
e. Explain answer d. Why did you get the results you did?
Data Table: Measured Angle q and Average Fhill will be found in Procedure I. Fgravity, FN, and q calculated Will be found in calculations section. Fill in the data table with red numbers.
Measured Angle q Average Fhill Fgravity FN q calculated
______________ __________ _______ _______ __________
______________ __________ _______ _______ __________
______________
__________
_______ _______ __________
Calculations:
1. Show the calculations you will use to determine the following data table points. No need to show me any "work". All I want to see is the formula you came up with to determine each one. I will plug-n-chug your values to see if your formulas work. (write your formulas after the = sign in RED)
a. Fgravity =
b. FN =
c. q calculated =
Questions:
1. Finish this statement: “As angle q increased, Fhill _________” (increased, decreased or stayed the same)
2. Finish this statement: “As angle q increased, FN _________” (increased, decreased or stayed the same)
3. Finish this statement: “As angle q increased, Fgravity _________” (increased, decreased or stayed the same)
4. If you were to hold the ramp at such an angle so that the 500 g mass just barely sat there (it didn’t slide, but was about to slide if you raised it just a hair’s breath more), what would be true about the relationship between Fms and Fhill?
5. What does the sharp increase in force represent when you first started to pull on the block?
6. True or False: mgsinq = Fhill. (Try it out on your data)
Rolling friction/Work Lab
50 points
Purpose:
To determine the amount of work needed to pull a wheeled cart up a hill.
Procedure I:
1. Plug a Force Probe into channel 1 of the Logger Pro box and set it for +/- 10N
2. Open Logger Pro on the computer. You must plug in the device BEFORE opening Logger Pro on the computer so it will recognize the equipment. Click on the y-axis numbers and MANUAL set it for -1N to 10N. Click on the x-axis and MANUAL set it for 0 to 20 seconds.
3. Set up a ramp as illustrated in the diagram below: Measure angle q (use that "high priced" protractor on the side of your ramp) because we are going to use Physics formulas later to solve for it. We want to see how close we were. Record your Angle q in the data table below. Notice the height of the ramp will NEVER CHANGE. But the ramp length (hypotenuse) will.
4. Hold the Force Meter so that it is straight on to the cart (as shown in the above diagram).
5. Holding very still, hit the collect button on the computer wait about 3 seconds and then pull that cart up the hill to the top of the table. The force you are collecting is the Fhill on that cart (Fhill = hypotenuse of the triangle.)
6. Use the mouse arrow to highlight at least 100 data points and then hit CTRL-C on the computer to copy those data points onto the computer’s clipboard. We are NOT interested in the TIME, just the Force (N). (You might have to copy both - the computer might not let you just copy just the one column. But, when you paste it into Excel, you can just ignore the Time data)
7. Open Excel.
8. Paste the 100 Force (N) data points into Excel and find their average. (In Excel, click on an open field box and write the following: =average(a1:ax) (Where “a” is the column name and “x” is the last number in the row series) Record this average as Fhill on your data table below.
9. Return to Logger Pro (the program that runs the Force detector) and click on the DATA bar and select “store latest run”.
10. Record the Distance your cart traveled up the ramp on your data table. (This is length (l) according to the diagram above. Notice that there is a centimeter ruler along the side of the track itself! Cool!
11. Change the angle q of your ramp. Go to a steeper angle. Repeat Steps 4-10.
12. Change the angle q one last time and repeat steps 4-10.
Procedure II
1. Open GA and make a Force v. Distance Graph for Trial #1 (the first angle you did). The first point is 0, Fhill because we need a reference point of Fhill at no distance. The second point will be Fhill v. Distance. Make sure you title your graph, label the axis and show units on the axis. If you don't know how to do this, refer to the GA help on my website.
2. Integrate the area under the curve and put the answer in your data table as Area under GA curve . For Trial #1. This area had better equal the work you found, correct?
3. Paste a copy of your graph here. You will have three graphs all together because you are doing this lab at three different angles.
Data:
Angle q q calculated Fhill Fgravity FN Distance Work Area under GA curve
_______ ______ ______ ______ _____ ______ ______ ____________
_______ ______ ______ ______ _____ ______ ______ ____________
_______ ______ ______ ______ _____ ______ ______ ____________
Calculations:
1. Show the calculations you used to determine the following data table points. No need to show me any "work". All I want to see is the formula you came up with to determine each one. I will plug-n-chug your values to see if your formulas work.
a. Fgravity
b. FN
c. q calculated
d. Work (Hint: Make sure you indicate - with a subscript - which Force you are talking about)
Questions:
1. What are the units for Work “broken down” (in other words, don’t use Newtons!)
2. True or False: If you drive up a steep hill to the top of a mountain, it takes the same amount of work as if you drive up a gentle grade (but reach the same height).
3. Would it take the same amount of gasoline to get up a steep grade as a gentle grade? Explain your answer.
4. True or False: In order to do work, something must move.
5. What does the sharp increase in force represent when you first started pulling the cart?
6. True or False: In rolling friction, the average forcehill when the cart is at a constant velocity is the same as if it were sitting still. But for sliding friction, the average forcehill on the block is greater when it is in motion than when it is sitting still (you must have completed both labs in order to answer this question correctly)
7. True or False: mgsinq = Fhill. (Try it out on your data)
What is due for this lab?:
1. Write all answers in red right next to where they are written in the document (if you are sending it to me via e-mail). Otherwise, just write the heading for each section that needs an answer and write it on one sheet of paper. Let's not waste paper! Don't Print out this lab! I was able to write all of the answers on one sheet of paper front and back. Then a separate sheet can be used for the GA graphs.
2. Write the names of all of the group members for this lab. Bold type the person who wrote this one up.
3. If you are sending it to my e-mail (gyyoung@capousd.org) you should save it as an MS Word document and send it with your initials in the title: eg. Mine would be "gywork".