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Friction

# Materials Required

•     Wooden block
•     50 or 20 g slotted weights
•     Horizontal plane (table top) fitted with a frictionless pulley at one end
•     Weight box
•     Spring balance

# Real Lab Procedure

• Find the mass of the wooden block by using a spring balance and place it on the table fitted with a frictionless        pulley at one end.
• Tie one end of a thread with the hook of the wooden block and pass it over the pulley.
• Tie the other free end of the thread to the weight hanger and let it hang vertically.
• Increase the mass, till the block just starts sliding when tapping the table.
•  Note the total mass added to the weight hanger and multiply it with acceleration due to gravity, g to get the            total weights added and record them in the observation table.This gives the force of limiting friction, F.
•  The normal reaction, R is given by the mass, M of the wooden block multiplied by acceleration due to gravity, g.
•  Repeat the experiment with different masses on the block and in each case is calculated and it is found to be       a constant for  the given pair of surfaces.
• Plot a graph taking normal reaction, R along X axis and limiting friction, F along Y axis. The graph will be a      straight line sloping upwards.
• The coefficient of friction is also calculated by measuring the slope of the graph.

$\mu =\frac{AB}{OA}$

# Simulator Procedure (As performed through theOnline labs)

• Select the material of the block from the 'Block material’ drop down list
• Select the material of the surface to perform the experiment from the ‘Surface material' drop down list.
• Use the ‘Block Weight’ slider to change the weight of the block.
• A thread is fixed at one side of the block and passes over a pulley.
• Use the ‘Hanging Weight’ slider to change the weight attached at the other end of the thread.
• The block moves towards right according to the addition of mass attached at the other end.
• A graph is plotted automatically with normal reaction along X axis and limiting friction along Y axis.
• The mass of the block and attached weights are noted.
• Now, calculations are done as per the observation column and the coefficient of friction of the block can be found out.
• Enable the ‘Show result’ checkbox to view the limiting friction, normal reaction, and coefficient of friction of the selected block.
• Click on the ‘Reset’ button to redo the experiment.

# Weight of the wooden block, W =...................g wt

Table for finding coefficient of friction

 No of Observations Weight on wooden block W(g wt) Normal Reaction R=W+w(g wt) Total weights on weight hanger= Limiting frictionF(g wt) Co efficient of friction $\mu \, =\, \frac{F}{R}$

From graph, coefficient of friction can be calculated as , $\frac{AB}{OA}$=--------

# Result

1.     Since F/R is a constant, the value of limiting friction is directly proportional to normal reaction.
2.     By calculation, Coefficient of fiction between given surfaces, µ =-------.
3.     From graph, Coefficient of fiction between given surfaces, µ =-------.

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