Slippery As an Eel

Slippery as an Eel

Problem

What is the coefficient of friction and how can it be determined?

Materials

A smooth block .approximately 2" x 4" s 5", a smooth board. 1" x 6" x 4 '. protractor. ring stand. clamp. pulley. spring balance, weight set, and various materials chosen from plexiglass. sandpaper. aluminum. rubber, cork, carpet, wax paper, styrofoam. and linoleum.

Procedure- Part A

Place the wood block on a flat surface. Attach a string to the block and nm it over the pulley and attach a weight to the string which is just large enough to move the block at a constant velocity, or in other words, enough to overcome friction. Weigh the block, then repeat using the same apparatus, only add a 500 g weight to the block. Then add a 1000 g weight to the block. Turn the block on is side and repeat. Finally, Using the other surfaces, such as plexiglass, sandpaper, aluminum, rubber. cork. carpet, wax paper. styrofoam, and linoleum, attach a weight to the string which is just large enough to overcome friction.

BOARD

BOOK

Part B

Now elevate the smooth board by supporting it with a support attached to a ring stand. Increase the elevation until the block slides down the plane at a constant speed. Using a protractor measure the angle of the board with the horizontal and record its value. Repeat this process using the other surfaces you used before. Also repeat using 500 g weight and the 1000 g weight. Calculate the normal force from the force diagram. Note that the vectors show the forces on the block.

Record your data for Parts A B in a data Table ( Include: Types of Surfaces, Force to move the block, Force to keep it moving. Normal Force, Force of Kinetic Friction, Force of Static Friction, and Coefficient of Friction)

Analysis

1.How do the coefficients of sliding friction compare to the inclined plane?

2.What variables seem to affect the coefficients sliding friction?

3.How does the coefficient of sliding friction compare on the horizontal and inclined surfaces?

4.What are your general conclusions regarding coefficient of sliding friction on a surface?

Coefficients of friction must be given for two materials, not one. Therefore there is no coefficient of friction for steel for example. There is a coefficient at friction for "steel on steel". If we think this way it is not realistic two have all coefficients of frictions for all material pairs listed. However, if you mean whether there is any list for at least some material pairs (especially those we face with everyday life) then you can look up in: CRC Handbook of Physical Quantities, Boca Raton: CRC Press, c1997, p 145-156. Some textbooks also have some limited amount of data, for example, this is - what you can find in Serway Physics for Scientists and Engineers, 4th -edition (p. 126.):

.
Coeff. Of Static / Coeff: of KineticKinetic
Materials / Friction / Friction
µs / µk
Steel on Steel / 0.74 / 0.57
Aluminum on Steel / 0.61 / 0.47
Copper on Steel / 0.53 / 0.36
Rubber on Concrete / 1.0 / 0.8
Wood on Wood / 0.25-0.5 / 0.2
Glass on Glass / 0.94 / 0.4
Waxed wood on Wet / 0.14 / 0.1
snow
Waxed wood on Dry / - / 0.04
snow
Metal on Metal / 0.15 / 0.06
(lubricated)
Ice on Ice / 0.1 / 0.03
Teflon on Teflon· / 0~04 / 0.04
Synovial joints in / 0.01 / 0.003
humans