Post on 16-Apr-2017
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