Measuring some coefficients of friction

Block on a ramp

Get the friction blocks and an aluminum ramp. Put a block on the aluminum ramp and tilt the ramp until the block just starts to slide. Measure the critical angle when the block starts to slide. Use the angle to calculate the coefficient of static friction between the block and the aluminum ramp. Try different surfaces of the block and estimate the coefficient of static friction for each different surface.

Next, tilt the ramp until the block slides. Take your stopwatch and measure the time. Use your kinematic equations to determine the net acceleration of the block. Then use the net acceleration to determine the coefficient of kinetic friction.

Block on a flat surface

Set up your laptop computers and LabPro force sensors on your table.

Grab a different experiment file: go to the folder

      My Computer -> 
         Student Shares on svphy01 -> 
            University Physics Students -> 
               Team Physics 311 -> 
                  Lab Pro

and drag onto your desktop the file drag_block_mwr.

Pick just one of the force sensors. Replace the rubber bumper on it with the hook.
Get one of the wooden "friction blocks" from the instructor. These blocks are covered with a fabric on two faces, and have a hook attached to one end. Also take out two of the heavy mass bars from your equipment set.
Measure the mass of the "friction block" and each of the mass bars.

Now, place the block on the aluminum ramp (flat on the table), motionless. Tie one end of a short piece of string to the block's hook, and the other end of the string to the force sensor's hook. It may help to put one of the massive weights on top of the friction block. Be sure to do the following every time you want to make measurements:

first, click on the "Zero" button while the string is loose; this re-sets the sensor to read "0 Newtons" when there is no force acting
then, click on the "Collect" button to start reading the force sensor

After you have started collecting data, wait for a second or two (you should see some data start to appear on the graph), then very gently pull on the force sensor. The computer will display the force with which you are pulling the block.

If you apply a very small force, the block won't move. In this situation, you are measuring the force of static friction between block and aluminum ramp.

If you apply a larger force, the block will start to slide. If you continue to pull as the block moves with a constant speed, you are measuring the force of kinetic friction between block and aluminum ramp.

Your job is to use the measured forces to figure out as many of the following as you can:

coefficient of static friction between wood and aluminum ramp.
coefficient of kinetic friction between wood and aluminum ramp.
coefficient of static friction between fabric and aluminum ramp
coefficient of kinetic friction between fabric and aluminum ramp
Try rotating the block so that you make measurements when the wide face is touching the aluminum ramp, and when the narrow face is touching the aluminum ramp.
do the coefficients of friction change depending on the area in contact with the aluminum ramp?
Try placing one heavy mass bar on top of the block and repeat your work. Then do it again with two heavy mass bars on top of the block.
do the coefficients of friction change depending on the total mass of the object?

Compare the coefficient of friction estimated using the flat ramp and the tilted ramp. Are they in agreement?

You must hand in

a neat table showing all your measurements
a sample equation showing how you convert the measured forces to coefficient of friction
a second neat table showing the coefficients of friction you have determined
an answer to the questions "What factors DO affect the coefficient of friction?" and "What factors do NOT affect the coefficient of friction?"

Do your answers to these questions agree with the description of friction in your textbook?