Page 62 - Physics - XI

Observations

Least count of the spring balance = _____ g wt
Zero correction of the spring balance = _____ g wt
Observed weight of the wooden block = W = _____ g wt
0
Corrected weight of the wooden block = W = _____ g wt
Observed weight of the pan = w = _____ g wt
0
Corrected weight of the pan = w = _____ g wt
Table for calculation of F and R
L
S. No. Weight on the Normal reaction Weight on the Limiting F
L
wooden block R = (W + P) pan friction. Ratio, R L
P X F = (w + X) (coeffi cient of
L
(g wt) (g wt) (g wt) (g wt) friction)
1.

2.
3.

4.
5.

6.

Graph

Plot a graph between normal reaction R along X-axis and the force of limiting friction F along Y-axis.
The graph would be a straight line as shown in Fig. 9.2. Y L
The slope of the straight line is a measure of coeffi cient
of friction (μ ) between the given two surfaces. From
graph, L

F F F G B
µ L = L G H
R
R
D R C Scale used:
Result Force of limiting friction (F L ) (in g wt) X- axis: 1 cm = ...g wt
1. The graph between F and R is a straight line as Y- axis: 1 cm = ...g wt
L
shown in Fig. 9.2. It shows that the magnitude A
of the limiting force of friction (F ) is directly H E
L
proportional to the normal reaction (R). X
C D
2. The value of coeffi cient of friction between the Normal reaction (R)
wooden block and the glass surface is _____ . (in g wt)

Fig. 9.2: Graph between R and F
Precautions L
1. The pulley should be oiled to make it frictionless.
2. Tapping should be gentle.

3. The glass plate should be clean, dry, and perfectly horizontal.
4. The string should be inextensible.

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