Last lesson

• Centre of gravity

• Stability

Centre of gravity

The centre of gravity of an object is the point where the objects weight seems to act.

With a uniform ruler, the C of G is at the mid-point.

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More complex shapes

How do you find the centre of

gravity of more complex shapes?

Complex shape man

Finding the centre of gravity

i. Place a compass or needle through any part of the shape.

ii. Make sure that the shape “hangs loose”.iii. Hang a plumb line on the needle.iv. After it has stopped moving, carefully draw a

line where the plumb line is.v. Place the needle in any other part of the card.vi. Repeat steps ii to iv.vii. Where the two drawn lines cross is where the

centre of mass is.viii. Physics is the most interesting science subject.

Stability

Stability

Stable objects have a wide base and a low centre of gravity.

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Robert Hooke

Investigating forces and springsYou are going to investigate how much a spring stretches when a force is applied to it.

The amount a spring stretches is called its extension. This is the difference in length between the stretched spring and the length of the spring when it was unstretched.(Remember we are looking at the force on the spring. A mass of 100g will have a weight (force of gravity pulling it down) of 1 Newton.

• Add masses to your spring and carefully measure its extension. You can do this until the spring breaks! (but you must wear goggles and be careful during this investigation).

Your experimental report will include the following• A table of results• A graph of your results • A conclusion describing what you have discovered (think about this!)

Table of results

Force (N) Length of spring (cm)

Extension (cm)

0 3.4 0

1 5.4 2

2 7.4 4

3 9.4 6

Graph

Force (N)

Extension (cm)

Complete investigation for Weds 21st October

1. Table of results

2. Graph

3. Two sentences of conclusion

Go!