1. TURNING EFFECT
OF FORCES

2. Moment Turning effect of a force about a pivot is called moment.
Everyday examples of moment
Opening a door

3. Losing and tighten nut using spanner or wrench
Lifting a load with wheelbarrow

4. Lifting a heavy object using crowbar/lever

5. Moment of a force can be calculated by using the formula:
Moment of a force = force × perpendicular distance from pivot to force
m = F × d
Unit of moment is Newton meter (Nm) or
Newton centimeter (Ncm)

6. The moment of a force can be increase:
by applying higher force
increasing perpendicular distance from pivot

7. Worked example Ans: moment = F × d moment = 50 × 0.25 = 12.5 Nm
A boy loses the nut using 0.25 meter long spanner. He applied 50N of force on the spanner. Calculate the moment of a force produce.
Ans: moment = F × d
moment = 50 × 0.25 = 12.5 Nm

8. Principle of moment
If an object is in equilibrium: the sum of the clockwise moments about any point is equal to the sum of the anti-clockwise moments about that point.
total clockwise moment = total anti-clockwise moment
F × d = F × d

9. Conditions for equilibrium
When a beam is balanced, we say that is in equilibrium. If an object is in equilibrium:
the force on it must be balanced (no resultant force)
the turning effects of the forces on it must also be balanced (no resultant turning effect).

10. The diagram shows a uniform half-metre rule balanced at its mid-point.
Worked example:
The diagram shows a uniform half-metre rule balanced at its mid-point.
What is the weight of the metal block?
Ans: F × d = F × d
F × 20 = 100 × 15
F = 100 × 15 / 20 = 75 N

11. Centre of gravity (centre of mass)
Centre of gravity (mass) of a body is the point about which the entire weight (mass) of the body seems to act.
The centre of gravity may be regarded as the point of balance.
The centre of gravity of a body is in the same position as its centre of mass.

12. The centre of gravity of regular and uniform (made all of the same material) objects are at their geometrical centers’.
For a uniform ruler, C.G is at the centre and when supported at this point it balances and when supported at any other point it topples.
C.G
C,G

13. Centre of gravity of certain objects lies outside the actual material of the object.
Cut a letter “L” out of a metal or plywood and stick on a sheet of thin paper to complete the rectangles as shown in the figure below

14. Finding center of gravity of irregular shape lamina
You are provide with
Irregular lamina
Thread and a bob
Nail clamped in a stand
Procedure:
Make three hole A, B and C on the lamina. First hang it on the point A, so that it can swing freely on a nail clamped in a stand. To locate the vertical line through A tie a plumb line to the nail as shown above.

15. When the plumb line comes to the rest, draw line of plumb line by using ruler and pencil. Mark it as line AD as shown below.
Then repeat the same procedure with point B and C, Where the line AD, BE and CF intersect is the center of gravity of the lamina as shown below.

16. What is the position of centre of mass of the tractor?

17. Stability
Ability of returning its original position after pushed and then released is stability of an object.

18. Stability can be increased by
Lowering the centre of gravity of the object
Increasing the base area of the object
Racing cars low centre of gravity and
a wider wheel base for higher
stability

19. Which of the following glass is more stable?