Coefficient of Friction Printer Friendly Version
Kinetic Friction

steel plates

In this phase of your experiment you will need one long steel plate, one short steel plate, one spring scale, and two 500-gram masses. After calibrating your spring scale, place the short steel plate (rough side down) on top of the longer plate at one end. Then use the string to drag it to the other end at a constant velocity. As you drag the plate, keep the string parallel to the surface of the table and observe the spring scale reading. Repeat three times and record your average reading. Next center a 500-gram mass on the top of the short plate and drag is once again at a constant velocity across the longer plate. Repeat this process three times and record your average spring scale reading. Finally, place two 500-gram masses on top of the short plate and drag is once again at a constant velocity across the longer plate. Repeat the process three times, and record your average spring scale reading in the data table given below.

Data Table I (plate sliding at a constant velocity)

 massin grams average springscale readingin newtons
 steel plate alone
 steel plate w/500 g
 steel plate w/1000 g

EXCEL will now assist with analyzing your data. Minimize your browser, double click My Computer, double click the shared drive called colwell/bay on Lederman, double click your period's folder and then finally double click 1-friction_steel.xls. You will most likely be asked to open the file as "read only" - that is fine. As soon as the file is open, use File Save As to rename the file as

LastnameLastnameFrictionSteel.xls

in your period's folder. This copy of the file now belongs uniquely to your group. Remember that there are to be no spaces in the file name. A printout of this file should be turned in with your lab report.

 What is the name of your file?

Refer to the following information for the next question.

For the situation illustrated above, when the plate has both 500 gram masses on top of it, check off which force(s) would belong on a freebody diagram of the plate.

Summary Questions

 What was your average coefficient of kinetic friction?

 Why should the coefficient of friction have been the same in all three trials?

 Explain the conditions that may have caused your worst trial's percentage difference?

wooden block

In this phase of the experiment you will need one long wooden board (to serve as an incline plane), one block of wood with one side covered in Teflon, two 200-gram masses, and a meter stick. Place the wooden block (Teflon side down) at one end of the board and measure the distance the block will slide down the board. Then lift the board slowly and record the height above the table when the block first starts to slip. Once the block starts moving, slightly lower the board until the block appears to be move at a constant velocity down the incline. Repeat three times and record the average heights in the table below. Next repeat the experiment three times with a 200-gram mass placed on the block and then again with 400-grams on the block.

Data Table II (block sliding down the incline)

 massin grams average heightto start slipping average heightto slide at aconstant velocity
 wooden block
 block w/200 g
 block w/400 g

EXCEL will assist with analyzing your data. Minimize your browser, double click My Computer, double click the shared drive called colwell/bay on Lederman, double click your period's folder and then finally double click 1-friction_wood.xls. You will most likely be asked to open the file as "read only" - that is fine. As soon as the file is open, use File Save As to rename the file as

LastnameLastnameFrictionWood.xls

in your period's folder. This copy of the file now belongs uniquely to your group. Remember that there are to be no spaces in the file name. A printout of this file should be turned in with your lab report.

 What is the name of your file?

Refer to the following information for the next question.

For the situation illustrated above, where the wooden block has one 200 gram mass on top of it, check off which force(s) would belong on a freebody diagram of the block.
 A B C D E F, G, H

Summary Questions

 What was your average coefficient of kinetic friction?

If you had not lower the height of the incline (its angle of inclination) once the block initially started to slip, what behavior would the block have displayed as it moved down the incline?

 According to your data, how did the angle that allowed the block to slide down on the incline at a constant velocity vary with the amount of mass placed on the wooden block? Explain.

Static Friction

In this section of the experiment you will use your knowledge of obtaining the coefficient of kinetic friction on an incline plane to determine the coefficient of static friction between two layers of sand. First fill up a cup with dry sand and slowly pour it onto a piece of paper covering the top of your lab station. Repeat until you get a "nice cone" of sand. Trace out the perimeter of the sand cone and proceed to measure the cone's circumference and height. Once your measurements are completed, return the cup and sand to the white bucket. You will be asked to turn in your "tracing paper" with your lab report.

 What was the perimeter of your sand cone?

 What was the height of your sand cone?

 Using trigonometry, what was the value for the coefficient of static friction between two layers of sand?

Your completed lab report will include a title page, a printout of your EXCEL worksheet for the steel plates, a printout of your EXCEL worksheet for the wooden block, and your tracing paper with its calculations for the coefficient of static friction for sand.