APPARATUS REQUIRED
i) A meter scale
ii) Slotted weight
iii) Stand
iv) String
v) Unknown body
THEORY:
Principle of moment:
It states that when a body in equilibrium is under the action of numbers of forces, then the moment of these forces about any point is zero. That is sum of clockwise moments. The principle may be utilized to find the magnitude and direction of an unknown force acting on a body in equilibrium. In the diagram if F₁ and F₂ be two forces acting at A and B of the right body is in equilibrium about the point 0. Then by principle of moment F₁ = OB = F₂x0A
If a unbrown weight ‘W’ is suspended at the end A of a meter scale and known weight ‘Wo’ be suspended at the end B as shown in fig, and then position of the point O(i.e. fulcrum) is so, adjusted than the meter scale is in equilibrium. From the principle of moments, we have.
W x OA = Wo xOB
W= OB/OA x Wo
therefore, w= b/a xWo
OBSERVATION:
| No.of obs | Weight on the armOA OB F₂ (gm) F1(cm) | Distance of CG from points (A and B)OA OB(cm) (cm) | Clockwise momentOA x F2(gm.cm) | Anticlockwise moment OB x Fi(gm.cm) | Result |
| 1 | 10 20 | 20 10 | 200 | 200 | |
| 2 | 100 50 | 10.1 20 | 1010 | 1000 | |
| 3 | 100 20 | 6.1 29.9 | 610 | 598 | |
| 4 | 50 20.2 | 10 25 | 500 | 512.5 | |
| 5 | 150 20 | 6 45.6 | 900 | 912 |
Table 2: For unknown weight.
| No.of obs. | Known weight Wo (gm) | Unknown weight on right arm (w) OA OB unknown Weight (w)= OA/OB xWo gm(a) | Unknown weight on left arm (w) OB OA unknown Weight (w)= OA/OB xWo gm(b) | Mean of (a)and(b)(gm) | Final mean weight (gm) |
| 1 | 10 | 7 32.6 46.57 | 28 6 46.67 | 46.62 | |
| 2 | 20 | 9.2 21.4 46.52 | 23.4 10 46.8 | 46.66 | |
| 3 | 50 | 20 18.7 46.75 | 30 32.4 46.30 | 46.52 | 46.605 |
| 4 | 100 | 32.5 15 46.15 | 4.7 10 47 | 46.575 | |
| 5 | 150 | 50 15.6 46.8 | 6.2 20 46.5 | 46.65 |
The weight of the unknown body measured by the beam balance
(W) = 46.89gm
RESULT
From this experiment we conclude that when a body is acted on by a number of forces under equilibrium the sum of the clockwise moment and the anticlockwise moment about a point are equal. Also the weight of an unknown body is found to be 46.605gm.
Sources of errors
1. The thread tied to the meter rod may not be exactly at the CG of it.
2. The meter rod may not exactly be at equilibrium due to external causes like fan, wind, etc.
3. At the point of equilibrium, the meter rod may not be exactly horizontal.
4. Error may be due to carelessness of the experiment.
PRECAUTIONS:
1. The C.G. of the meter red should be carefully marked. The meter rod must be allowed to rest on a sharp edge exactly at its C.G.
2. The weight should be suspended away from C.G.
3. In the position of equilibrium, the meter rod should be horizontal.
4. The thread should be tied exactly at the C.G. of the meter rod
5. Experiments should be performed carefully.