EXPT NO: 05. STATIC FRICTION
Aim: To study the
relationship between force of limiting friction and normal reaction and to find
coefficient of static friction between a block and a horizontal surface.
Apparatus: Rectangular wooden block with hook, string,
rough, balance, weight box, pan, horizontal plane surface with pulley.
Diagram:
Formula : Coefficient of static friction = 
where P is the effort and 'W is the Load. 
= Coefficient
of static friction
= Coefficient
of static friction
Procedure
:
Note the weight of wooden block W0 and empty pan
P0 separately using rough balance.
Keep the wooden block on horizontal surface. Tie one end of string to the
hook of theblock, pass the string over pulley and connect its free end to the pan. The string should be parallel to the horizontal plane.
Add the weight gradually to the pan till the block just begins to move on
horizontal plane. Note the weight (P1) in the pan. Find the total effort (P= P0 +P1) required to move the wooden block (load)
Place a weight of 50 g on the block and repeat the above procedure. Take
five readings by increasing the weight on block by steps of 50 g. calculate the
coefficient of static friction using the formula.
Plot the graph of effort (P) along Y-axis and load (W) along X-axis.
Calculate the slope which gives the value of coefficient of static friction
jas.
Observations :
1)
Mass of the block, W0 =…………….gmwt
2)
Mass of the pan, P0 =…………….gmwt
3) Acceleration due to gravity, g = 980
cm/s2
|
Sr.no
|
Mass
on the block W0 gmwt
|
Total
load
(W=
W0 +W1)gmwt
|
Mass
in the pan P1
gmwt
|
Total
Effort
(P=
P0 +P1)
gmwt
|
Coeff.
of static friction
 |
Mean Coeff. of static friction
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01
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02
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03
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04
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05
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Calculations:
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Observations
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1
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2
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3
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4
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5
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Log
(P) = a
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Log
(W) = b
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(a
- b) = c
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 = Antilog of c |
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Graph :
Result :
1)
Coefficient of static friction by calculation =…………….
=…………….
2) Coefficient of static friction by graph, =…………….
=…………….
Precautions :
The string (between block
and pulley) should be parallel to horizontal plane.
The pan should hang freely
without touching the table.
Starting position of the block
must be same for all readings.
Clean the horizontal
surface and wooden block with blotting paper (or cloth paper)
J K L
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