Question

Q5: Explain in brief the principle of moments through the figure given below. ​

Answer 1

The principle of moments state that for an object to be in equilibrium, the sum of clockwise moments about a pivot must be equal to the sum of anti clockwise moments about the same pivot. However, in this context we simply see that moments is calculated by taking the magnitude of force applied multiplied by the perpendicular distance the force is being applied to the pivot point. This means a large weight at a small distance from the centre of the pivot can have the same moment as a lighter object at a larger distance from the pivot. Hence this is why both people on the see saw are in equilibrium, balanced and not experiencing movement.

Answer 2

The principle of moments states that for an object to be in equilibrium, the sum of clockwise moments about a pivot must be equal to the sum of anti clockwise moments about the same pivot. In the figure, the weight of the small child (W_1) is acting at a distance d_1 from the pivot, and the weight of the large child (W_2) is acting at a distance d_2 from the pivot. For the seesaw to be in equilibrium, the moment of the small child must be equal to the moment of the large child.

The moment of a force is the product of the force and the perpendicular distance from the line of action of the force to the pivot. In other words, it is a measure of the tendency of the force to rotate the object about the pivot.

The clockwise moment of the small child is given by:

M_1 = W_1 * d_1

The anti-clockwise moment of the large child is given by:

M_2 = W_2 * d_2

For the seesaw to be in equilibrium, the sum of clockwise moments must be equal to the sum of anti clockwise moments. Therefore:

M_1 = M_2

W_1 * d_1 = W_2 * d_2

This means that the weight of the small child multiplied by their distance from the pivot must be equal to the weight of the large child multiplied by their distance from the pivot.

In the figure, the small child is sitting closer to the pivot than the large child. Therefore, the small child must be heavier than the large child in order for the seesaw to be in equilibrium.