Science Form 2

FIS CIE Year 8A & YF

3rd Term, 2011/2012

Stability of an object

This is the point at which the whole weight of the body can be taken as acting through

Centre of Gravity

The geometrical centre of some common shapes

This is also where the centre of gravity and the object’s weight, W, can be considered to act

Regular and uniform objects

When more than one material makes up an object the centre of gravity will be affected.

For non-uniform shapes

When more than one material makes up an object the centre of gravity will be affected.

For non-uniform shapes

For some objects the CG is not located on the actual object

External CG

Ring

Stool

2 uniform perpendicular planks

This happens when the planks are of unequal

masses. Which do you think is more massive, kids?

When an object is suspended, so that it can swing freely, it will come to rest with its CG vertically below the point of suspension

When an object is suspended

Find the CG of an irregular shaped lamina

CG of an irregular shape

a

bc

a bc

b

a

c

plumb line

hole

Pin held by clamp

Now, try to balance the object at that point…

Balancing Act!

a b

c

An object is stable if it can return to its original position when tilted and released

An object is unstable if it cannot return to its original position when tilted and released

Stability

The Traffic ConeA great example of a VERY stable object.

What features of the cone make it so stable?

- Low Centre of Gravity

- Wide base

The position of the Centre of GravityThe Base Area

Factors that affect stability

The position of the Centre of GravityThe Base Area

Factors that affect stability

The position of the Centre of GravityThe Base Area

Factors that affect stability

Lowering the Centre of GravityIncreasing the Base Area

Improving STABILITY

Each of the diagrams on the right represent a Double Decker bus with passengers inside.

Draw out and label the one which shows all passengers on

- the lower level- the upper level- both levels

The Double Decker Bus

If more people sit upstairs on the bus, the CG will rise/fall. This will make the bus more stable/unstable and it can be tilted by a greater/lesser angle

The bus will fall over when the CG acts inside/outside of the bus’ base

A stable object has a low/high CG and a narrow/wide base

Delete a word to complete the sentences

Pair Do Activity 9.3 in your textbookComplete the worksheets [will be given to

each pair]

Activity Time