Notes on Moment | Grade 9 > Science > Machine | KULLABS.COM

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#### Moment of Force

When a force is acted on a body, it results in either displacement of the body or its rotation about a point or axis. This rotation or turning effect of force may be clockwise or anticlockwise.

The turning effect of the force acting on a body about an axis is called the moment of the force.

The moment of the force is equal to the product of the magnitude of the force and the perpendicular distance of the line of action of the force from the axis of rotation or fulcrum. Mathematically,

Moment = F × S

Here, F= force applied

S= perpendicular distance of the line of action of the force from the fulcrum

The SI unit of a moment is Nm but Ncm is also in use. If the force is not applied perpendicular on a lever, the value of moment decreases.

#### Law of moment

The law of moment states that “In the equilibrium condition of the lever, the sum of the anticlockwise moment is equal to the sum of the clockwise moment”

(Anticlockwise) (Clockwise) • The SI unit of moment is Nm
• The law of moment states that “In the equilibrium condition of lever, the sum of the anticlockwise moment is equal to the sum of the clockwise moment”.
• The moment of the force is equal to the product of magnitude of the force and the perpendicular distance of the line of action of the force from the axis of rotation or fulcrum.
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### Very Short Questions

Moment of force is the turning effect of force acting on a body about an axis. It is affected by two factors:
Amount of force
Perpendicular distance from pivot to the line of action of force.

The moment of force about a point is the product of force and the perpendicular distance from the pivot to the line of action of the force. i.e. Moment = F × s Unit = Nm

A tall tree has a longer perpendicular distance than that of the short tree which gives bigger turning effect in the tall tree. So, a tall tree has the greater probability of breaking than a short tree during storm.

When a person moves towards the end of the branch, its perpendicular distance with respect to the pivot goes on increasing which results in the increase of turning effect. Hence, probability of breaking of a branch of a tree increases.

When handle is fixed on the outside edge of a door, the perpendicular distance with respect to the pivot increases, which results in the increase of turning effect. Hence, it makes it easy to open the door.

It is because a long spanner has long handle such that we can increase the perpendicular distance from the point of application of force to the pivot, result in the increment in the turning effect to the rusted knot. Hence, it is used to open a rusted knot.

Given ,
Load distance (L.d) = 40cm = 0.4m
We have,
Moment of load = L x Ld = 200 x 0.4 = 80 Nm
If the equipment is in equilibrium, moment of load must be equal to the moment of effort.
∴ Moment of effort = 80 Nm

Given,
Effort (E) = 20N
Effort arm (E.a) = 20cm = 0.2m
Moment of effort = ?
By using formula,
Moment of effort = E x E.a = 20 x 0.2 = 4Nm
Hence, the moment produced is 4Nm.

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• ### What does friction do to simple machines?

increases velocity ratio
increases efficiency
no effect on velocity ratio
Decreases velocity ratio
• ### Law of moment applies to ______.

lever at any state

lever at equilibrium

First class lever

All levers

• ### The turning effect of the force acting on a body about an axis is called ______.

movement

inertia of force

locomotion

moment of force

• ### Which one of the following is the correct law of moment?

anti-clockwise moment is not equal to clockwise moment

anti-clockwise moment is twice of the clockwise moment

anti-clockwise moment is half of the clockwise moment

anti-clockwise moment is equal to clockwise moment

• ### What is formula of moment?

moment= force × perpendicular distance

moment= force × velocity

moment= force /velocity

moment= force / perpendicular distance