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A lever is a rigid bar that pivots around a fixed point, the fulcrum, to transmit forces. Free GCSE AQA Physics notes with key definitions and 14 FAQs.
Levers and Gears is part of Moments, levers and gears (physics only) in GCSE AQA Higher Physics.
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A lever is a rigid bar that pivots around a fixed point, the fulcrum, to transmit forces. Free GCSE AQA Physics notes with key definitions and 14 FAQs.
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Use this lesson to stay inside Moments, levers and gears (physics only) while connecting the detail back to the wider Forces topic.
Read the core explanations from Levers and Gears before testing yourself from memory.
You use a bottle opener to remove a cap. Your bike has gears to help you climb hills. Both work by transmitting forces - but how exactly do they make your life easier?
Levers and gears are simple machines that transmit forces and turning effects. They do not create energy, but they can multiply force, change the direction of a force, or change rotational speed. Understanding them helps explain everyday devices such as crowbars, bottle openers, bicycles, and hand tools.
Picture a seesaw with two children. The heavier child sits closer to the pivot point, while the lighter child sits further away. This balances because moments (turning effects) are equal on both sides.
Levers work on the same principle of moments. The moment of a force equals force × perpendicular distance from the pivot. For a lever in equilibrium: clockwise moments = anticlockwise moments.
The mechanical advantage tells you how much the lever multiplies your force. If mechanical advantage = 4, you only need to apply 1/4 of the load force. But there's a trade-off - you must move your end 4 times further.
Worked example: Calculating Mechanical Advantage
A lever has the fulcrum 0.2 m from a 500 N load and 1.8 m from where you apply effort. Calculate the effort force needed and mechanical advantage.
Answer: Effort force = 55.6 N, Mechanical advantage = 9.0
Gears are like levers wrapped around circles. When two gears mesh, the teeth ensure they rotate together without slipping. The gear ratio determines how rotational motion and force are transmitted.
When two gears mesh, they rotate in opposite directions. A small driver gear turning a larger driven gear makes the driven gear rotate more slowly but with a larger turning effect. If you need the final gear to turn in the same direction as the first gear, you can add an idler gear between them.
If the gear ratio is 4:1, the output gear rotates once for every 4 rotations of the input gear. This gives 4× the torque but 1/4 the speed. Just like levers, gears trade speed for force.
Worked example: Gear System Analysis
A motor gear with 20 teeth drives a wheel gear with 80 teeth. If the motor rotates at 1200 rpm, find the wheel's rotation speed and mechanical advantage.
Answer: Wheel speed = 300 rpm, Mechanical advantage = 4
| Feature | Levers | Gears |
|---|---|---|
| Motion type | Linear/rotational | Rotational only |
| Force transmission | Through rigid bar | Through meshing teeth |
| Mechanical advantage | Distance ratio | Teeth ratio |
| Common examples | Crowbar, scissors, pliers | Bicycle, car gearbox, clock |
| Main advantage | Simple, reliable | Precise speed control |
Both systems follow the same fundamental principle: they redistribute force and distance while conserving energy. Neither creates energy - they make it easier to apply force where and how you need it.
Levers can change the size or direction of a force by using moments about a pivot. Gears always transmit rotational motion, and adjacent gears rotate in opposite directions. Both systems trade force against distance or torque against speed rather than creating extra energy.
Exam questions often test your understanding of moments and mechanical advantage. Always start by identifying the fulcrum position and measuring perpendicular distances correctly.
For gear problems, count teeth carefully and remember the relationship between gear ratio, speed, and torque. If speed decreases, torque increases proportionally.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
A lever is a rigid bar that pivots around a fixed point, the fulcrum, to transmit forces. It multiplies effort by increasing the distance over which the force is applied, and works on the principle of moments.
A fulcrum is the fixed pivot point around which a lever rotates. The position of the fulcrum determines the mechanical advantage of the lever, such as in a crowbar or a bottle opener.
A gear is a toothed wheel that meshes with other gears to transmit rotational motion and force. Gears can change speed, direction or multiply torque, and the teeth make meshing gears rotate together without slipping.
Gears are toothed wheels that mesh to transmit rotational motion and force, with adjacent gears rotating in opposite directions. A small driver gear turning a larger driven gear makes it rotate more slowly but with a larger turning effect.
Levers work on the principle of moments: a rigid bar pivots around a fulcrum, and for equilibrium clockwise moments equal anticlockwise moments. Applying effort far from the fulcrum lets a small force balance a large load close to it.
Balance the moments to find the effort force, then divide load by effort. With a 500 N load 0.2 m from the fulcrum and effort 1.8 m away, effort = 100 ÷ 1.8 = 55.6 N, so mechanical advantage = 500 ÷ 55.6 = 9.0.
Gear ratio is teeth on the driven gear ÷ teeth on the driver gear, and output speed is input speed ÷ gear ratio. A 20-tooth motor gear driving an 80-tooth gear gives 4:1, so 1200 rpm becomes 300 rpm.
Bikes have gears to help riders climb hills, because gears trade speed for force. A larger turning effect at a lower rotation speed makes it easier to push the bike uphill, while energy is conserved.
Levers and gears do not create energy; they redistribute force and distance while conserving energy. A lever with a mechanical advantage of 4 needs only 1/4 of the load force, but the effort end must move 4 times further.
Two meshing gears rotate in opposite directions because their teeth push against each other. If the final gear needs to turn the same way as the first, an idler gear can be added between them.
A mechanical advantage of 4 means the machine multiplies the force by 4, so only 1/4 of the load force is needed. The trade-off is that the effort end must move 4 times further.
When a small driver gear turns a larger driven gear, the driven gear rotates more slowly but with a larger turning effect. With a gear ratio of 4:1, the output turns once for every 4 input turns, giving 4 times the torque at 1/4 the speed.
Levers transmit force through a rigid bar and can give linear or rotational motion, while gears transmit force through meshing teeth and give rotational motion only. A lever's mechanical advantage comes from a distance ratio, a gear's from a teeth ratio.
Examples of levers are a crowbar, scissors, pliers and a bottle opener. Examples of gears are a bicycle, a car gearbox and a clock. Both transmit forces and turning effects.