Levers, pulleys and gears are three simple mechanisms that make it possible to lift heavy objects without applying a very large force.
Lifting objects
Lifting heavy objects can be difficult, it takes a lot of force to lift them upwards because of the force of gravity pulling them down towards the ground. It is possible to make lifting objects easier by using mechanisms that allow you to apply less force. Three such mechanisms are levers, pulleys and gears.
Levers
A lever uses a bar, pole or beam and a pivot to make it easier to lift a heavy object. The pivot is the point that the bar, pole or beam balances on. If a small force is applied at one end of the lever, a much larger force is produced at the other end.
Example
If a heavy box needs to be lifted, a lever can be used as shown below. A small force can be applied at one end of the lever which produces a large enough force to lift the box upwards.
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Small force
2
Large force
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Pivot
Pulleys
A pulley uses a rope and one or more wheels that the rope runs over to make heavy objects easier to lift. Instead of picking the heavy object up and working against gravity, a smaller force can be applied downwards in the same direction as gravity to lift the object up more easily.
Example
A weight can be lifted by running a rope over a wheel attached to the ceiling. When the person pulls down towards themselves, the rope becomes tense and makes the wheel turn. This provides a larger upward force on the weight and allows the person to lift it more easily.
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Small force
2
Large force
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Rope
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Pulley
A two-wheel pulley makes it even easier to lift a heavy object, only half of the force needed with a single wheel pulley can be used to lift the object.
Gears
A gear is a wheel with teeth. Gears of different sizes can be used to rotate a heavy object. A small gear with less teeth rotates faster than a large gear with many teeth. The small gear needs less force to rotate than the large gear.
Example
Gears are used to rotate the hands of a clock. Different sized gears are used for different hands. Smaller gears rotate faster so they are used for the minutes hand. The larger gear is used for the hour hand as it rotates more slowly.
