Forces

Question 1

What is centre of gravity

Answer 1

• centre of gravity of an object is the point at which the whole weight of the object may be considered to act

Question 2

Turning effect of force( moment of a force )

Answer 2

• moment of a force is the turning effect of the force.
• it is equal to the product of the force and the perpendicular distance of the line of action of the force from the pivot

Question 3

What is a couple

Answer 3

• consists of two equal and opposite parallel forces whose lines of action do not coincide
• tends to produce rotation only

Question 4

What is the torque of a couple

Answer 4

• turning effect of a couple
• it is equal to the product of one of the forces and the perpendicular distance between the forces

Question 5

Principle of moments

Answer 5

• states that for a system in equilibrium, there is no resultant moment about any point
• sum of clockwise moment about any point must be equal to sum of anticlockwise moments about the same point
• total clockwise moments = total anti-clockwise moments

Question 6

Conditions for a system to be in equilibrium

Answer 6

• no resultant force
• no resultant torque about any point
  (For 3 non-parallel forces in the same plane, the lines of action of the forces must intersect at a common point)

Question 7

What is Hooke’s Law

Answer 7

• the extension of a body is proportional to the applied load,
• provided the proportionality limit is not exceeded

Question 8

Hooke’s Law formula and its WD

Answer 8

• F = kx
• WD = 1/2Fx = 1/2kx²