Do now! Can you write down on the piece of paper 3 things you learnt last lesson (there is a clue in the picture!)? WITHOUT looking in your books!

Do now! Can you answer the 5 questions on the piece of paper please? WITHOUT looking in your books!

Last lesson Know what the turning effect of a force is Know that the moment of a force depends on force and the distance from the pivot Know the principal of moments

The turning effect of a force depends on two things; The size of the force Obviously!

The turning effect of a force depends on two things; The distance from the pivot (axis of rotation) Not quite so obvious! Axis of rotation

Turning effect of a force The turning effect of a force is called the moment of the force Note the unit is Nm, not N/m! Moment (Nm) = Force (N) x distance from pivot (m)

A simple example! nut spanner (wrench) 50 N 0.15 m

A simple example! nut spanner (wrench) 50 N 0.15 m Moment = Force x distance from pivot Moment = 50 N x 0.15 m Moment = 7.5 Nm

What do you do if the nut won’t move and you can’t push harder?! nut spanner (wrench) 50 N 0.15 m

Get a longer spanner! nut spanner (wrench) 50 N 0.25 m Moment = Force x distance from pivot Moment = 50 N x 0.25 m Moment = 12.5 Nm

More than one force Take an uneven see-saw for an example I thought he didn’t like dogs? Only dead ones! pivot

If the see-saw is balanced, what must be the weight of the dog on the left? pivot 1.2 m2.2 m 110 N ? N

The force on the left is trying to turn the see- saw anticlockwise about the pivot pivot 1.2 m2.2 m 110 N ? N

The force on the right is trying to turn the see-saw clockwise about the pivot pivot 1.2 m2.2 m 110 N ? N

If the see-saw balances, the turning effect anticlockwise must equal the turning effect clockwise pivot 1.2 m2.2 m 110 N ? N Anticlockwise momentclockwise moment=

Anticlockwise moment = clockwise moment ? X 1.2 = 110 x 2.2 ? X 1.2 = 242 ? = 242/1.2 ? = N pivot 1.2 m2.2 m 110 N ? N Anticlockwise momentclockwise moment=

Principle of moments An object is in equilibrium when anticlockwise moments = clockwise moments YouTube - Alan Partridge's Apache office

30 second silent thinking time Do you have any questions?

What do these have in common? YouTube - Soccer-world cup 1986 by Diego Maradona(Argentina vs England

Today’s lesson Centre of gravity Forces on beam supports (start thinking about!)

Centre of gravity? He can be really boring sometimes.

Centre of gravity The centre of gravity of an object is the point where the object’s weight seems to act. I think he wants you to copy this

Centre of Gravity “Circus” Sketch and number each object and put a cross where you think the Centre of Gravity is.

Complex shapes How do you find the centre of gravity of complex shapes? Complex shape man

Position of centre of gravity

Draw the sentence

Write the drawing?

Self-assessment i. Place a compass or needle through any part of the card. ii. Make sure that the card “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 subject.

The ruler trick!

Let’s sit on a plank!

The ruler trick! Your homework is to explain how the ruler trick works in language simple enough that your imaginary 8 year old brother Jack could understand. Minimum 100 words, maximum 500 words. Due Friday 12 th November 2010.

Let’s try some questions Page 57 Questions 1, 2 and 3