Turning Effect of Forces

Question 1

Moment of a force, M

Answer 1

The product of the force and the perpendicular distance from the pivot to the line of action of the force.

Question 2

Couple

Answer 2

Two equal and opposite parallel forces whose line of action do not coincide.

Question 3

Principle of moment

Answer 3

When a body is in equilibrium, the sum of clockwise moments about a point is equal the sum of anti-clockwise moments about the same point.

Question 4

Centre of Gravity, C.G

Answer 4

The point at which entire weight of an object appears to act, for any orientation of the object.
The position of the centre of gravity of an object affects its stability.

Question 5

Stable Equilibrium

Answer 5

There is a restoring moment to tilt the object back to the original position

Question 6

Stable Equilibrium: CG

Answer 6

CG rises when it is tilted

Question 7

Stable Equilibrium: Vertical line through its centre of gravity

Answer 7

Falls within its base area

Question 8

Stable Equilibrium: After being displaced slightly

Answer 8

Object returns to its original position

Question 9

Unstable Equilibrium

Answer 9

There is an overturning moment to tilt the object further in the same direction.

Question 10

Unstable Equilibrium: CG

Answer 10

CG lowers when it is tilted

Question 11

Unstable Equilibrium: Vertical line through its centre of gravity

Answer 11

falls outside its base area

Question 12

Unstable Equilibrium: After being displaced slightly

Answer 12

falls outside its base area

Question 13

Design for stability

Answer 13

1. Lower its centre of gravity
2. Increase the area of its base