Chapter 8 Moment of force & Principle of moment of lever

Moment of force

1. The moment of force is the turning effect of

force on an object.

2. Formula:
• Moment of force = Force (N) x

perpendicular distance to the force (m).

• 3. The moment of force increase if:

a) Magnitude of force increases.

• b) perpendicular distance from pivot (fulcrum)

to effort increases.

Moment of force in daily life

Unit = Newton meter (Nm).



The Principle Of Levers

Load(N) x The distance of load = Force or x The distance of
from the fulcrum (m) effort from the
Effort(N) fulcrum (m)

Example of the principle of lever

1. What effort is required to keep the lever in balance?

Load(N) x The distance of L = xForce or The distance of E
from the fulcrum Effort(N) from the fulcrum
2N (m) (m)
E =Ex
x 30cm = 60 50cm
x 50 = 60 / 50
= 1.2N
E

Example of the principle of lever

2. Calculate the weight of the load.

Load(N) x The distance of L = xForce or The distance of E
from the fulcrum Effort(N) from the fulcrum
L (m) (m)
L = 4N x
x 40cm = 400 100cm
x 40 = 400/ 40
= 10N
L



Example of the principle of lever

A) B)

The distance of L Force or The distance of E
from the fulcrum Effort(N) from the fulcrum
x = xLoad(N)

(m) (m)

Example of the principle of lever

A)

Wx 80cm = x10N 60cm

xW 80 = 600
= 600/ 80
W = 7.5N

Example of the principle of lever

B)

x40N 45cm = xY 50cm

xY 50 = 1800
= 1800/ 50
Y = 36N

C) D)

The distance of L Force or The distance of E
from the fulcrum Effort(N) from the fulcrum
x = xLoad(N)

(m) (m)

C)

x250g 35cm = x500g Qcm
Qx
500 = 8750
Q
= 8750/500
= 17.5cm

D)

x =E 75cm x195N 25cm
E=
x195 25
E=
75

65N

• Exercise
• 1. calculate the weight of Ali needed to keep the see-

saw in balanced if the weight of Abu is 280 N.

Ali Abu

Ali x 2.5m = 280N × 1.5cm
Ali = 280 x 1.5
2.5
L = 168 N

• MODUL SAINS (pg 131)

The diagram shows a force of 5 N applied to a screwdriver
handle to open a tin lid.
What is the load of the screwdriver?

Load × Load distance = Effort × Effort distance

L x 2cm = 5N × 28cm
L = 5 × 28
2
L = 70 N

• MODUL SAINS (pg 131)

Determine the effort needed to push the load inside the
wheelbarrow.

1kg = 10N

Load × Load distance = Effort × Effort distance

E x 2m = 45kg × 0.5cm
E = 45 × 0.5
2
E = 11.25kg

E = 11.25 x 10
= 112.5N