Centre of Gravity

1. Centre of Gravity The centre of gravity (centre of mass) of a body is an imaginary point where the whole …………….. of the body seems to act in any orientation. • The CG of a regular object is at its …………... • The CG of an ……………….. object is determined using a plumb line. • If a body is hanging freely at rest, its centre of gravity is always vertically below the …………., thus the plumb line method works. It can only be used for ………….., irregular objects. pivot flat irregular weight centre

2. 09 August 2014 Stability Objective To understand what stability is and describe how the centre of gravity of an object affects it.

3. Outcomes • All must be able to carry out an experiment that shows how an objects shape affects its stability. • Most should be able to explain how the centre of gravity of an object effects its stability. • Some could be able to define the stability of an object and apply this definition to different situations.

4. http://www.youtube.com/watch?v=U45lggf2OkM • Why do you think that weebles wobble but they don’t fall down?

5. Stability • Stability is a measure of the body’s ability to maintain its original position. • What 2 things can change an object’s stability?

6. Stability • Stability is a measure of the body’s ability to maintain its original position. • The CG is lowered • The area of the base is really wide

7. Stability • Stability is a measure of the body’s ability to maintain its original position. • Explain why the stability of an object is improved if: • The CG is lowered • The area of the base is really wide

8. Stability • Stability is a measure of the body’s ability to maintain its original position. • Explain why the stability of an object is improved if: • The CG is lowered • The area of the base is really wide • Lowering the CG (A lower CG will allow the line of action to act within the base area of an object) • Area of its base should be as wide as possible (allow line of action to act within base area)

9. Definition • If the line of action of the weight of a body lies outside the base of the body there will be a resultant moment and the body will tend to topple.

10. Draw the diagrams and explain what will happen in each diagram (a), (b) and (c)

11. Weebles Wobble but they don’t fall down • Design a high chair that will not fall down very easily.

12. Part Route 23 CANONMILLS Y 226 TSC Centre of Mass Line of Action

13. Pivot Line of Action

14. Pivot Line of Action

15. Part Route 23 CANONMILLS Y 226 TSC • What happens to the centre of mass when all he passengers are on the top deck? • How would this affect the stability? Centre of Mass Line of Action

16. http://www.youtube.com/watch?v=U45lggf2OkM • Why do weebles wobble but they don’t fall down? • Draw a weeble and label it to explain why it doesn’t fall down.

17. High Chair design • Design a high chair that will not fall down very easily.

18. High Chair design • WWW • Is the design practical • Would it fall over easily • What else is good • EBI • How could the design be improved?

19. Practical Time!! • Stability Prac • Set up the equipment as above. • You have a selection of objects to try and topple. • You will place the objects at the bottom of the board and measure the angle at which it just starts to topple.

20. Stability PracticalResults Analysis: Explain which shape toppled first and which toppled last.

21. What have you learnt today? • How could what you have learnt today be useful?