Page 76 - Physics - XI

Calculations
m m m m
Mean mass, m 1 2 3 4 ..... g
4
Result

The value of the unknown mass m of the given body by using metre scale is _____ g.

Precautions

1. The edge of the wedge should be perpendicular to the graduation scale.
2. The wedge used for balancing the scale should have sharp edge and it should be perpendicular to the

length of metre scale.
3. The reading should be taken only when the metre scale becomes stable and in the horizontal position.
4. The known and unknown weights should not be so heavy as to bend the scale.

5. The centre of gravity of the scale should be determined accurately and the scale should be placed at
this position on the wedge.
6. Some part of the cotton thread over the scale should be kept along the graduations of the scale.

Sources of Error
1. The edge may not be sharp.

2. Metre scale may have faulty calibration.
3. The thread used may be thick and heavy.

VIVA VOCE

Q1. Is moment of force a scalar or vector quantity?

Ans. It is a vector quantity. The torque or moment of force rF .
Q2. For what angle, the torque will be maximum?

Ans.
rF
τ = rF sin θ, τ will be maximum when θ = 90°.

Q3. State principle of moment.
Ans. If a body is in equilibrium under the action of the number of forces in one plane, the sum of clockwise
moments is equal to the sum of anticlockwise moments.

Q4. What do you mean by 'moment of force'?
Ans. Moment of the force is the product of force and its perpendicular distance from the axis of rotation.

Q5. What is torque?
Ans. It is another term used for expressing moment of force.

Q6. What is the S.I. unit of moment of force?
Ans. Nm (newton metre)

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