Download Friction Lab

FRICTION and INCLINED PLANES
AP PHYSICS LAB
NAME ________________________
PURPOSE: After completing this experiment, you should be able to describe what factors affect the coefficient of friction
between two surfaces and measure the coefficient of kinetic friction on a flat surface and an incline.
EQUIPMENT: Inclined plane, spring scale, wooden block, sandpaper, string, platform balance, masses, flour.
PROCEDURE:
Set up your apparatus as seen in the diagram: Make sure your board is horizontal. Place the block on the larger (broader)
wood side.
block
string
Spring scale
Board (level plane)
Part 1: DIFFERENT MASSES: (Table 1)
3. Find the mass of your block by hanging it from a spring scale. Place this in data table 1.
4.
Pull the block so that it moves at a constant velocity across the board. Be sure to keep the scale parallel to the board.
Record your scale reading in the data table next to the mass of the block.
5. Place a 100 g mass on the block and find the force needed to pull the block at a constant velocity again. Repeat this 2 more
times, each time adding 100 g to the weight of the block. Record your scale readings in table 1.
Part 2: DIFFERENT SURFACES: (Table 2)
6. Again, place your block on the broad wood side with no masses on it.
7.
Pull the block so that it moves at a constant velocity, and record the scale reading
(trial 5). (This trial will be like trial #1!)
8. Place the block on the skinny wood side and repeat step 7 (trial 6).
9.
Repeat this procedure again with the sandpaper side (trial 7).
10. Replace the wood block with the metal slab. Place it on the board metal side down and pull it at a constant velocity.
Record these as trial 7.
11. Flip the metal slab over to the “non-metal side”. Some of these are sandpaper again, some are ceramic. Pull it as before.
Record this data as trial 8.
Part 3: INCLINED PLANE: (Table 3)
1. Set the incline at 5 and place your block onto the incline using the broad wood side.
2. Place the block at the bottom of the incline and pull the block by the scale up the incline at a constant velocity. Be
sure to keep the spring scale parallel to the inclined plane. Record the spring scale reading in table 3 as trial 9.
3. Repeat this procedure increasing the angle 10 each time. Record as trials 10-13 in table 3.
In your lab notebooks, please set up data and calculation tables like the ones shown below – you can cut and paste these
if you wish!
DATA TABLE 1: Different Masses
Trial #
Mass (g)
DATA TABLE 2: Different Surfaces:
Scale Reading
Trial
1
Surface type
Scale Reading
5
2
3
6
4
7
8
DATA TABLE 3: Inclined Plane
Trial
Angle of Incline
Scale Reading
9
10
11
12
13
CALCULATIONS: SHOW WORK FOR TRIAL # 1 AND TRIAL # 9 IN YOUR LAB NOTEBOOK UNDER
CALCULATIONS!
1. Find your weight by multiplying your mass (in Kilograms) by - 9.80 m/s2. (This is Newton’s second law: F weight = mass *
agravity)
** Wait to do these steps later. We will talk about them in class next week.
**2. Using the angle of the incline and your trig functions, find F parallel and F perpendicular.
** 3. Find your normal force from your weight or your perpendicular force.
4. Convert your scale force into Newtons, and enter it into the calculation table (done the same way you found weight in
step #1).
5. Using Fnet = ma, determine the friction force from the parallel and/or scale forces.
6. Using the equation,  = F friction/ F normal, calculate your coefficient of friction ().
**You will need to do this step once I return.
**7. Using Excel, plot a graph for trials 9-13 using the F normal as the x-axis and F friction as the y axis. Using the
trendline, find the slope of the graph and display this equation on the graph when you print it.
CALCULATION TABLE (All Parts): This should be included in your lab notebook in the same format:
Trial
F weight
F parallel
F perpendicular
F normal
F scale
F friction

1
2
3
4
5
6
7
8
9
10
11
12
13
QUESTIONS and CONCLUSIONS:
1.
2.
3.
4.
5.
6.
Draw a free body diagram of your block for parts 1 and 3. Be sure to include ALL forces acting on the block!!
From part 1, does the coefficient of friction change with the mass of the block? Explain.
From part 2, does the coefficient of friction rely upon the surface area in contact and/or the type of surface? Explain.
In parts 1 and 2, how was the frictional force related to your scale force? Explain using Newton’s Laws.
In part 3, how were the parallel, scale, and frictional forces related? Again, explain using Newton’s Laws.
From your graph, what does the slope of your line represent? What mathematical relationship is there between the
frictional force and the normal force?
7. How did the frictional force change with the angle in part 3? What ACTUALLY caused this change?
We WILL go over this lab before you need to turn it in, but you need to finish all data readings and begin putting this into
your lab notebook. Background should include (but not be limited too) all of Newton’s laws, a definition of each force
used, and the relationship between these forces if inertia is in effect plus any equations used. Don’t forget your error
analysis (no percentage error) and concluding statement(s).