Levers
When you use a spoon to prise a lid from a tin you are using a simple machine called a lever. In fact, levers are the basis of many tools in and around your house and work. Primary Connections has a Year 2 unit called Machine Makers, all about exploring how ramps, levers and pulleys are used to push and pull things all around us. For more diagrams and activities, download Machine Makers for free! How do levers work? First class lever In summary, in a first class lever the effort (force) moves over a large distance to move the load a smaller distance, and the fulcrum is between the effort (force) and the load. As the ratio of effort (force) arm length to load arm length increases the mechanical advantage of a first class lever increases. Archimedes referred to a first class lever in his famous quote "Give me one firm spot on which to rest (a fulcrum) and I will move the Earth". Second class lever In a second class lever the effort moves over a large distance to raise the load a small distance. As the ratio of effort (force) arm length to load arm length increases, the mechanical advantage of a second class lever increases. In a wheelbarrow, the closer the load is to the wheel, the greater the mechanical advantage. Nutcrackers are also an example of a second class lever. Third
class lever In a third class lever the load moves further than the effort (force) and the mechanical advantage is low, which is why it's difficult to apply great force to the load. This can be an advantage by not squashing sausages on the barbecue! When you lift a load using your forearm you are using a third class lever. Your biceps muscles are attached to the forearm just in front of the elbow. The load is on the hand, and the effort is between the fulcrum (elbow) and the load.
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