Poha Lab

Moment of a force:

The moment of force is a measure of its tendency to cause a body to rotate about a specific point or axis. This is different from the tendency for a body to move, or translate, in the direction of a force. In order for a moment to develop, the force must act on the body in such a manner that the body will begin to twist. This occurs every time a force is applied so that it does not pass through the android of the body. A moment is due to force not having an equal and opposite force directly along its line of action.

The magnitude of the moment of a force acting about a point is directly proportional to the distance of the net force from the point or axis. It is defined as the product of the force(F) and the moment arm (d). The moment arm or lever arm is the perpendicular distance between the line of action of the force and the centre of moments.
Moment =Force× perpendicular Distance from the pivot
or τ=F×d

The Principle of Moments:

The principle of moments states that “when in equilibrium the total sum of the anti-clockwise moment is equal to the total sum of the clockwise moment”. When a system is stable or balanced, it is said to be in equilibrium as all the forces acting on the system cancel each other out. In equilibrium, Total Anticlockwise Moment = Total Clockwise Moment Force,F1×Moment Arm, d1 = Force, F2×Moment Arm, d2

The principle of moments can be explained with the help of the following experiment.

MATERIALS REQUIRED:

Wedge.
Meter rod
Slotted weights
Thread

weights

Slotted weights

Procedure

Suspend the meter rod at the 50 cm mark so that it is balanced horizontally. The meter rod is said to be in equilibrium. The 50 cm mark is the pivot.
Suspend a mass, m1, from one side of the ruler a distance, d1, from the pivot. Read the distance d1 in cm, from m1 to the pivot. Record in a suitable table. Record the value of mass m1 in kg in the table too.
Suspend a second mass, m2, from the other side of the pivot. Carefully move this mass backward and forward until the meter rod is once more balanced horizontally. Read the distance d2 in cm from the mass m2 to the pivot. Record d2 in cm, in the table, along with the mass m2 in kg.
Repeat several times using different masses and distances.
Calculate the turning forces, F1 and F2, using W = mg.
Calculate the clockwise and anticlockwise moments.

PRECAUTIONS

Ensure that the surface on which you place the wedge is stable and on the same level. This will help in achieving accurate measurements and maintaining the equilibrium of the system.
Check the zero reading of the meter rod and make necessary adjustments if needed, before starting the experiment.
To improve accuracy and reliability, repeat the measurements multiple times and calculate the average. This will help reduce the random error.

1. State the principle of moments as applied to a lever:

Force, F1×Moment arm, d1= Force, F2×Moment arm, d2

Force, F1= Force, F2

Moment arm, d1= Moment arm, d2

Force, F1× Moment arm, d2 = Force, F2× Moment arm, d1

2. The moment of a force of 10N about a fixed point O is 5N m. Calculate the distance of the point O from the line of action of the force.

0.5m

0.005m

3.A 10 N force is applied at a distance of 1 m from the hinge of door such that the line of action of force is parallel to the plane of the door. The moment of force produced on the door is

100Nm

0Nm

0.1Nm

10Nm

4. When is the moment of forces positive?

When the forces rotate the body in clockwise direction.

When the forces rotate the body downward.

When the forces rotate the body upward.

When the forces rotate the body in anticlockwise direction.

5. The moment of a force about a given axis depends:

Only on the magnitude of force.

Only on the perpendicular distance from the axis.

Neither the force nor on the perpendicular distance from the axis.

Both on the force and the perpendicular distance from the axis.

Physics

Verify the principle of moments by using a metre rod balanced on a wedge