calculate coefficient of friction by plotting graph between load and effort required
Answers
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
Thread
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.
Simulator Procedure (As performed through the Online 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.
Observations
Weight of the wooden block, W =...................g wt
From graph, coefficient of friction can be calculated as , =--------
Result
Since F/R is a constant, the value of limiting friction is directly proportional to normal reaction.
By calculation, Coefficient of fiction between given surfaces, µ =-------.
From graph, Coefficient of fiction between given surfaces, µ =-------.
Explanation:
Friction occurs in two ways: kinetic and static. Kinetic friction acts on an object that slides on a surface, whereas static friction occurs when friction prevents the object from moving. A simple but effective model for friction is that the force of friction, f, is equal to the product of the normal force, N, and a number called the coefficient of friction, μ. The coefficient is different for every pair of materials that contact each other, including a material that interacts with itself. The normal force is the force perpendicular to the interface between two sliding surfaces -- in other words, how hard they push against each other.