Do now Can you read the hydraulics pages of your books (p157)?

Today’s 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 principle of moments

What happens when you try to open a door with one finger? Where do you push? Hi, my name is Mr Stick hinges

Do you push near the hinges? I can’t do it!

Do you push far from the hinges? That’s easier!

Moments – Turning forces

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 The moment is calculated by multiplying the force by the distance from the pivot

Turning effect of a force – moment of a force Moment (Nm) = Force (N) x distance from pivot (m) Note the unit is Nm, not N/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 Do you think we’ll be safe in this power point? It’s not looking good! 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=

Rotational Equilibrium When there is no resultant moment on an object (when anticlockwise moments = clockwise moments) we say the object is in rotational equilibrium. YouTube - Alan Partridge's Apache office

Whew! We seemed to have survived the power point pivot

Don’t speak too soon! pivot BOMB

pivot BOMB

pivot BOMB

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pivot

Nice one!

pivot You’ll have to do some questions now, or he’ll kill me too!

pivot Read pages 162 and 163 and make notes. Then try the questions.