Levers

Why is the Door Handle on the opposite side to the hinge?

The Turning Effect of Forces

A force can turn something in a circular path.

What determines how easy it is to turn the bolt?

The length of the wrench/spanner determines the 'turning force', called the moment.

Levers

A lever is a device which changes the direction of a force. It can be used as a force multiplier.

A lever has a pivot/fulcrum.

http://en.wikipedia.org/wiki/File:Palanca-ejemplo.jpg

The See-Saw

A child of 30kg sits on the seat 6m from the end of a see-saw. Where must an adult of 60kg sit so that the see-saw is balanced?

http://upload.wikimedia.org/wikipedia/commons/9/94/Stick_Figure.svg

60kg

6m

3m

Moments

A moment of force can be calculated using the formula:

Moment of force = Force * distance from pivot.

Eg: A force 20cm from the fulcrum of a lever balances the weight force of a 2kg object which is 5cm from the fulcrum. How strong must the force be? Hint: be careful with units!

Physics Now

31-35, pages 41-42

First Class Levers

First class levers are force multipliers.Having the load close to the fulcrum will have a high mechanical advantage.Having the load far from the fulcrum will have a low mechanical advantage.Examples include scissors, can opener, elbow etc.

http://edu.glogster.com/media/4/33/57/52/33575263.gif

Second Class Levers

Second class levers go in this order.FulcrumThen LoadThen EffortExamples include nut crackers, wheel barrows and your jaw.They are force multipliers which make our job easier.

http://commons.wikimedia.org/wiki/File:Nut_cracker.jpg

http://commons.wikimedia.org/wiki/File:Gray1003.png

Third Class Levers

Third class levers are speed multipliers which means a lot of force can occur in a small area.Third class levers go in this order:FulcrumThen EffortThen Load

http://blog.stack.com/wp-content/uploads/Screen-shot-2011-04-22-at-11.24.02-AM.png

Summary

Class of LeverOrderExamples