Can you give me an experiment to calculate the coefficient of static and dynamic friction?

Answer 1

Get a block of known mass, a protractor and a board; the materials should be chosen as those for which you want to find the friction coefficients. Place the block on the board and gradually increase the angle of the board while keeping track of the angle the board makes with horizontal. The angle at which the block slips is crucial. The friction force opposes the movement of the block based on the normal force applied on the block by the board. As you increase the angle, the normal force decreases. F = uN where F is the friction force, N is the normal force and u is the coefficient of friction, in this case, static. Using the angle at which the block slips, calculate N; N = m sin(@) where m is the mass of the block, and @ is the measured angle. Now F must be equal to the force of gravity pulling on the block parallel to the board, otherwise the block would slip (and it does precisely at the measured angle) so; F = m cos(@) where m is the mass of the block and @ is the measured angle. Now that F and N are known, use the aforementioned relationship to calculate u. This value should be non-negative and has no units. As for dynamic friction; let the block slide from the top of the board when it is at a high angle and gradually decrease the angle until the block comes to a stop on the board due to friction. This should be done in trials of larger degrees until a working angle is found, then more precise trials can commence. When such an angle is found that any higher angle allows the block to keep going all the way to the bottom, the same calculations as above must be repeated to find the coefficient of dynamic friction.

Answer 2

To measure the coefficient of static friction, you can set up an inclined plane with a block on it. Slowly increase the angle of the plane until the block just starts to move. Measure the angle and use trigonometry to calculate the coefficient of static friction.

For dynamic friction, you can place the block on a horizontal surface and attach a spring scale. Apply a force parallel to the surface and slowly increase it until the block moves at a constant speed. Use the spring scale reading and the normal force to calculate the coefficient of dynamic friction.