Purpose: To study sliding friction and to determine the coefficients of static and kinetic friction.
Theory: Friction is a force that opposes motion. Static friction prevents an objects being set into motion by an external force. Kinetic friction opposes the progress of a sliding object. Static friction is given by Fs< usn where N is the normal force between the object and its support surface and us is the coefficient of static friction. There-fore, the coefficient of static friction is given by Us= fs, max/ N
Where F s, max is the maxixmum force of static friction. Once the external force overcomes static friction, the object moves. Its motion is opposed by kinetic friction. The force of
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2. With the block on one of its broad sides, run the string over the pulley. Adjust the string to ensure that it is level. Attach the mass holder to the free end of the string. 3. Find the mass on the mass holder that will allow the block to slide at constant speed once it is set into motion. Record this value as fk. 4. Add enough mass to the mass holder such that the block begins to move on its own accord. Record the mass as Fs. 5. Repeat steps 2 through 4 for the other three sides of the block. 6. Return the block to its original orientation. Repeat steps 2 through 4 four times with an additional 50 to 100 grams added to the block. Record the mass added to the block as m added. Data Record And Analysis: mb = 242.4g Side | M added | N | Fk | Fs | Uk | Us | Side 1 | 0 | 242.4 | 80g | 80g | .33 | .33 | Side 2 | 0 | 242.4 | 80g | 100g | .33 | .41 | Side 3 | 0 | 242.4 | 80g | 80g | .33 | .33 | Side 4 | 0 | 242.2 | 60g | 80g | .25 | .33 | Side 1 | 50g | 292.4 | 80g | 110g | .27 | .30 | Side 1 | 70g | 312.4 | 90g | 100g | .29 | .32 | Side 1 | 90g | 332.4 | 110g | 120g | .33 | .36 | Side 1 | 100g | 342.4 | 120g | 150g | .35 | .44 | Average (Side 1) | | | | | 0.31 | .3525 | Conclusion: The frictional force is affected by the surface type and weight. It is not affected by the surface