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Static Friction and Limiting Equilibrium

By Krysshan1920 Feb 18, 2012 465 Words
Destiny Stuart
Partner’s Name: Shanygne Swann

Lab Report #2

Title of Experiment: Static Friction and Limiting Equilibrium

Brief Theory of Experiment: In limiting equilibrium, the sum of the forces on block X and on the hanging masses (load) Y is zero. The load is increased to a value until block X just slides at constant speed when the table is tapped. Tapping the table destroys the limiting equilibrium condition momentarily by altering the balance between tension (T) in the string and the maximum force Ff (max). It is left for you to show that the coefficient of static friction is µs= mass of load/ mass of block + added masses...

Brief Account of the Method: The mass of a block was determined and a string hung over a pulley is attached with a holder at the end. Enough mass was added to holder to move the block at a constant speed when the table was tapped. The mass of the holder plus the masses added to it were recorded along with the mass of the block. The experiment was reset and additional masses were added to block. The experiment was then repeated.

Experimental Data:

M=M1 + added masses| m=hanging masses +50g| m/M|
Empty block =208.7| 100| 0.479|
Empty block +200g=408.7| 200| 0.489|
Empty block + 400g=608.7| 300| 0.4928|
Empty block +600g= 808.7| 400| 0.4946|
Empty block + 800g= 1008.7| 500| 0.496|
Empty block +1000g= 1208.7| 600| 0.4964|
Empty block+1200g= 1408.7| 700| 0.4967|

Graph and Calculations:
Graph attached


Discussion: Sources of error included the tension of the string changing due to tapping the table and the intensity of the tap varied.
Precautions taken for this experiment included taking the ratio of the mass of load to the mass of the block and additional masses to ensure all values were in the same range. Also, only one person’s judgment was used to determine when the block was moving at a constant speed.

One suggestion would be to repeat the experiment for each mass of block and additional masses to ensure results are as accurate as possible. A critical look at my results showed that the mass of the load increased as the mass of the block and additional masses increased. By definition µs= hanging mass/mass of block and additional masses i.e µs= m/M. From the graph value of µs = 0.5 which falls into the normal range of static friction which is from 0.3 to 0.6. Because the value of µs is less than 1.0 which implies that the force required to move the block along the table is less than the normal force of the table on the wooden block.

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