Moments of force
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MOMENT OF FORCE
If a body under the action of a net external force is allowed to rotate about a pivot, the body will tend to turn in the direction of the applied force.
Examples of turning effect of force:
· A person pushing a swing will make the swing rotate about its pivot.
· A worker applies a force to a spanner to rotate a nut.
· A person removes a bottle’s cork by pushing down the bottle opener’s lever.
· A force is applied to a door knob and the door swings open about its hinge.
· A driver can turn a steering wheel by applying a force on its rim.
The moment of a force or torque, r is defined as the turning effect of the force about a pivot and is the product of the force (F) and the perpendicular distance (d) from the line of action of the force to the pivot.
A moment of a force is basically, a quantity which represents the rotational effect caused by a force when applied to a body at any other point than its centre of gravity or is pivot point.
By, Newton's third law, this force has an equal and opposite reaction at the point of pivot or its CG.
Moment of force, mathematically, is the product of this force and perpendicular distance between the line of action of the forces.
It's the force multiplied by ”the perpendicular distance between the line of action and the axis of rotation.” A force times a distance has the dimension of work, so it is the work being done to keep an object rotating.
The Moment of a 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 the force. In order for a moment to develop, the force must act upon the body in such a manner that the body would begin to twist.
Suppose there is a door . these are the hinges, you are standing in front of the door. Choose any two points on the door, one near the hinge, the other at the handle. (hint: let them be along the straight line.). Applying the same amount of force, try to open the door pushing/pulling it.
Consider the figure above. Given that the cat weighs 150 N and the distance from the cat to the pivot is 30 cm, calculate the moment of force about the pivot.
Why is it easier to open the lid of a container with a spoon than a coin?
Examples of turning effect of force:
· A person pushing a swing will make the swing rotate about its pivot.
· A worker applies a force to a spanner to rotate a nut.
· A person removes a bottle’s cork by pushing down the bottle opener’s lever.
· A force is applied to a door knob and the door swings open about its hinge.
· A driver can turn a steering wheel by applying a force on its rim.