The load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement — a small contraction of the biceps produces a large movement of the forearm.
This type of lever system also gives us the advantage of a much greater speed of movement. Many muscle and bone combinations in our bodies are of the Class 3 lever type. Laws of motion that scientists use today were proposed by Sir Isaac Newton He is regarded by many as the greatest influence in the history of science, and the newton measurement of force acknowledges his contribution. His laws enable people to make predictions.
In the examples above, the effort and load forces have acted in opposite rotation directions to each other. If a load tries to turn the lever clockwise, the effort tries to turn the lever anticlockwise. Forces acting on a lever also have different effects depending how far they are away from the pivot. For example when pushing a door open it is easier to make the door move if you push at the door handle rather than near to the hinge pivot.
Pushing on the door produces a turning effect, which causes rotation. The force is measured in newtons and the distance to the pivot is measured in metres or centimetres, so the unit for torque will be either newton metres Nm or newton centimetres Ncm.
You can increase the amount of torque by increasing the size of the force or increasing the distance that the force acts from the pivot. Forces from our muscles produce torques about our joints in clockwise and anti-clockwise directions. If the torques are equal and opposite, the lever will not rotate. If they are unequal, the lever will rotate in the direction of the greater torque.
In this diagram below, the load and weight of the lower leg produce a clockwise torque about the knee. The lower leg will rotate in a clockwise direction. If the hamstring muscle at the back of the upper leg contracts with a strong force, it produces an anticlockwise torque that holds the leg up. In this diagram, lifting the weight like the person on the left produces a greater torque about the lower spine pivot — the lifting force is at a greater perpendicular distance to the pivot.
Levers are used all over the place in our everyday life. But have you ever wondered just exactly how they work? A lever works by reducing the amount of force needed to move an object or lift a load. A lever does this by increasing the distance through which the force acts. In this experiment, you will show that the closer the fulcrum — or the pivot point of the lever — is moved toward the load, the less effort is required to lift the load.
At the same time, the distance over which you must apply the force increases. You will see that levers neither increase nor decrease the amount of total effort necessary. Instead, they make the work easier by spreading out the effort over a longer distance. They will help with the fulcrum placement. Put your marbles, weight or rock into the cup labeled LOAD. Tape your binder clip, flat side down, onto a stable, flat surface.
Start by placing the lever arm onto the binder clip 4 inches from the end marked LOAD. The lever converts the little force of your hand at one end to a large force at the other end; large enough to do a big job.
But it does this at the cost of a larger distance. You must therefore push on the one end of the lever for a longer time than you would have to without the lever.
According to the work energy theorem, the amount of work you do on a system becomes the energy contained in the system. Because the work is constant with or without the lever, the energy is also constant. A lever therefore does not create energy. The energy inputted to do a certain job is exactly the same with or without the lever. The lever just maximizes efficiency.
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