Module 3 - Equilibrium

Question 1

Define Centre of Mass

Answer 1

The point where the mass of an object acts

Question 2

Define Centre of Gravity

Answer 2

The point where the weight of an object acts

Question 3

What are factors that affect the stability of a object

Answer 3

• Having a wider base (as it increases the tilt required to make the CoG act outside of the base)
• Having a lower centre of gravity (as it would take more tilt to act outside of the base)

Question 4

How to find the Centre of Gravity for uniform objects

Answer 4

• Find where the lines of symmetry of the object meet

Question 5

How to find the Centre of Gravity for non-uniform objects

Answer 5

• Suspend object from a pin and it will naturally hang stationary about its CoG.
• Draw a line vertically down the pin
• repeat this for another point on the object
• The CoG will be where the two lines meet

Question 6

Why might some objects Centre of Gravity not act through its middle

Answer 6

If the distribution of the mass of the object is not uniform.

Question 7

What is a Moment

Answer 7

The turning effect of a force.

Question 8

What is the equation for Moments

Answer 8

The Moment of a force = The Perpendicular Distance (of the line of action of the force) from the pivot X The Force

Question 9

What is the unit for Moments

Answer 9

Nm [Newton-Metre]

Question 10

What is the Principle of Moments

Answer 10

“For a system in Equilibrium, the sum of the clockwise moments are equal to the sum of the anti-clockwise moments”

Question 11

How do you find 2 Forces of opposing direction from a Moments system when both are unknown

Answer 11

Take 1 of the unknown forces to be the pivot and use the principle of moments to find the other force
- Repeat for the 2nd Force or use knowledge of the resultant force to find the 2nd Force