Moment Bar Experiment

Moment Bar Experiment


To find the mass of a body using a metre scale


A metre scale, slotted weights, given body etc


By principle of moments, M x AG = W x BG (see figure)

M = (W x BG)/AG --------------------- (1)

Where, M = mass of the given body and W = weight suspended.


The centre of gravity of the metre scale is found out first. The scale is then suspended, using a stand and string loop, at the centre of gravity, G (in this position the scale remains horizontal). The given body is suspended at a suitable position, say A. On the other side of G a suitable weight (W) is suspended. Its position is adjusted so that the scale again remains horizontal. Let B be the position of W. The length AG and BG are noted. Now the mass of the body is calculated using the relation (1). This procedure is repeated by changing weights (W). The mean mass of the body is then determined.

Observation Table and Readings

Centre of Gravity, G = 49.2 cms

Mean mass of the body, M = 247.96 x 10-3 kg


1. Define centre of gravity

Ans: The centre of gravity of a body is the point through which the entire weight of the body acts, disregarding the position.

2. Define mass

Ans: Mass of a body is the amount of matter contained in it.

3. Define weight

Ans: Weight of a body is called as the force in which the earth attracts the body towards its centre.

4. What is meant by moment of a force?

Ans: The turning effect produced by a force on the body, on which it acts is called moment of a force.

5. What is meant by clockwise moment?

Ans: The moment of a force where its effect is to turn or rotate the object in the same direction in which the hands of a clock circulate is called clockwise moment.

6. What is meant by anticlockwise moment?

Ans: The moment of a force, where its effect is to turn or rotate the object in the opposite direction in which the hands of a clock circulate is called anticlockwise moment.

7. Give one application of moments.

Ans: Levers

8. What is the principle of the moment bar?

Ans: The principle of moment. That is, the algebraic sum of the moment of the forces acting on a rigid body is zero.

9. Why do you suspend the metre scale at the centre of gravity to find the weight of a body?

Ans: In order to make the moment of the weight of the scale about the point of suspension zero.

10. Can you find the relative density of a body using moment bar.

Ans: Yes

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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