Chapter 4 - Forces in Action

Question 1

What is the centre of gravity?

Answer 1

The centre of gravity of an object is a point where the entire weight of the object seems to act

Question 2

What is the centre of mass?

Answer 2

The centre of mass of an object is a point where the entire mass of the object seems to be concentrated

Question 3

What is unique about a uniform gravitational field?

Answer 3

The centre of mass is the same place as the centre of gravity

Question 4

What is another definition of the centre of mass or gravity?

Answer 4

The centre of mass or centre of gravity of an object is the point through which a single force has no turning effect on the body

Question 5

What happens when the line of action of force is applied to the centre point?

Answer 5

When an externally applied force is put through the centre point, it produces a straight line motion, but no rotation

Question 6

Where does a freely suspended object come to rest?

Answer 6

It comes to rest with its centre of gravity vertically below the point of suspension

Question 7

What makes an object more stable?

Answer 7

Objects with wide bases and low centre of mass are more stable

Question 8

Where does the centre of mass lie?

Answer 8

Centre of mass will lay exactly where all lines of symmetry cross

Question 9

What is a stable object?

Answer 9

A stable object will not fall over given a small push, and the centre of mass remains above the base

Question 10

To which direction do objects fall?

Answer 10

Objects fall towards the side which the centre of mass lies past the pivot

Question 11

How is the centre of mass found in a practical?

Answer 11

Suspending the body from a position near its edge by making a hole and sticking a rod through it Allow it to come to rest
Draw a line vertically down, using a plumb-line to guide
Repeat the process from another point
Centre of mass lies where the lines cross