refer these References:
- http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/using_physics_make_things_work/moments/revision/3/
- http://gleeson9science.pbworks.com/w/page/7537618/SM%202
- http://www.msichicago.org/online-science/activities/activity-detail/activities/simple-machines-build-a-lever/
- http://bvg8science.wikispaces.com/The+Lever+-+Krisco
- https://sites.google.com/a/mystma.org/ms-hamann-s-science/simple-machines-energy
- http://je012.k12.sd.us/3rd%20grade/Simple%20Machines.htm
- http://gtt-sot-wms.wikispaces.com/Old+Day+03+-+Simple+Machines
- http://www.sagadbl.com/2012/05/levers-science-form-2-chapter-10.html
- http://www.youtube.com/watch?v=yhrR4384SGE
- http://www.youtube.com/watch?v=zD1N6MyoeeM
- http://www.youtube.com/watch?v=M6xLglhs3rs
.