# Turning Effect of Forces

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- TURNING EFFECT OF FORCES MOMENTS
- Lesson Objectives
- Identify what are the forces that will give rise to clockwise / anticlockwise moments

- Calculate clockwise / anticlockwise moments

- Use the principle of moments to solve problems.

- MOMENTS What is moments? A force can cause many things to move or stop. When a force causes an object to turn, this turning effect is called moments. Example: A person sitting on a see-saw.
- MOMENTS What is moments? A force can cause many things to move or stop. When a force causes an object to turn, this turning effect is called moments. Example: A person sitting on a see-saw.
- Types Of Moments
- There are 2 types of moments:

- Clockwise moment

- Anticlockwise moment

- Types Of Moments
- There are 2 types of moments:

- Clockwise moment

- Anticlockwise moment

- Clockwise Moment When a force causes an object to turn in a clockwise direction, it is called a CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
- Clockwise Moment When a force causes an object to turn in a clockwise direction, it is called a CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
- ANTI-Clockwise Moment When a force causes an object to turn in an anti-clockwise direction, it is called a ANTI-CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
- ANTI-Clockwise Moment When a force causes an object to turn in an anti-clockwise direction, it is called a ANTI-CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
- CALCULATING MOMENTS Moment = force ? perpendicular distance between force and pivot In symbols: Moments = F ? d Weight => F d Unit for moments: Newton-metre (Nm)
- Example 1: A cat of weight 20N stands on one end of a see-saw and the distance between the cat and the pivot is 3m, find the moment. Solution: In this case the cat is causing a clockwise moment. Clockwise moment = F x d = 20 x 3 = 60 Nm F = 20N d = 3m
- Example 2: A duck stands on one end of a see-saw, 5m away from the pivot. If the weight of the duck is 10N, find the moment. Solution: The duck’s weight is causing an anticlockwise moment. Anticlockwise moment = F x d = 10 x 5 = 50 Nm F = 10N d = 5m
- Examples which is the distance? Where is the force & pivot? F d d F F d d d F F
- weight weight Principle of Moments For an object to be in equilibrium(stable/not moving), the total clockwise moment must be equal to the anticlockwise moment about the same pivot point. pivot It is the fixed(non moving) point
- SOLVING PROBLEMS RELATED TO PRINCIPLE OF MOMENTS Step 1: Identify what are the forces that will give rise to clockwise / anticlockwise moment Step 2: Find the clockwise / anticlockwise moment Step 3: Equate the clockwise and anticlockwise moments
- Find the value of d. WORKED EXAMPLE 10N 30N 6m d
- Step 1: Identify what are the forces that will give rise to clockwise / anticlockwise moment
- Find the value of d. WORKED EXAMPLE Anticlockwise moment Clockwise moment 10N 30N 6m d
- Step 2: Find the clockwise / anticlockwise moment
- Clockwise moment = Force x distance between force and pivot = 30 x d = 30d Nm WORKED EXAMPLE Anticlockwise moment Clockwise moment Anticlockwise moment = Force x distance between force and pivot = 10 x 6 = 60 Nm Find the value of d. Solution: 10N 30N 6m d
- Step 3: Equate the clockwise and anticlockwise moments
- Find the value of d. Solution: Clockwise moment = Force x distance between force and pivot = 30 x d = 30d Nm Anticlockwise moment = Force x distance between force and pivot = 10 x 6 = 60 Nm Using the principle of moments, Clockwise moment = Anti-clockwise moment 30d = 60 d = 60 ? 30 d = 2 m WORKED EXAMPLE Anticlockwise moment Clockwise moment 10N 30N 6m d
- Points to note:
- The unit for force must be in Newtons, the unit for distance must be in metres.

- The distance must measured from the force to the pivot.