What is a gear and how does it work?

A gear is a toothed wheel. When its teeth lock into the teeth of another gear, turning the first gear pushes the second one round, passing movement and force from one wheel to the next.

Why do two gears spin in opposite directions?

When two gears mesh directly, the pushing tooth of one drives the gap of the other from the outside. That means if one turns clockwise, the gear next to it is forced to turn anticlockwise.

Why does a small gear spin faster than a big gear?

A small gear has fewer teeth, so it must turn more times to match the larger gear's teeth as they mesh. The small gear spins quickly while the big gear turns slowly but with more force.

What is a gear train?

A gear train is three or more gears lined up so all their teeth touch. Turning any one gear makes the whole row turn together, letting machines send motion across a distance.

Where are gears used in everyday life?

Gears are inside clocks, bicycles, egg whisks, hand drills, toy cranes and car engines. They let machines trade speed for strength or change the direction of turning.

How Gears Work Together

Science Interactive lesson Free to play

A gear is a wheel with teeth cut around its edge. When the teeth of two gears lock into each other — called meshing — turning one gear forces the next one to turn too, so motion and force pass from wheel to wheel. This simple idea is how clocks, bicycles, hand drills, egg whisks and car engines pass power from one part to another.

Two important rules follow from meshing. First, two gears that mesh directly always turn in opposite directions: if one spins clockwise, its neighbour spins anticlockwise. Second, gear size changes the trade-off between speed and turning force. A small gear has fewer teeth, so it must spin faster to keep pace with a larger gear, while the big gear turns more slowly but with greater force.

Line up three or more gears so every pair of teeth touches and you have a gear train — turning one gear drives them all. Understanding gear ratios, meshing and the speed-versus-strength trade lets you explain why a bicycle has different gears for flat roads and steep hills.

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Meet the gears

⚙️🔧⚙️ How Gears Work Together Gears are wheels with teeth around the edge. When their teeth lock together, one gear can push the next gear to spin! Watch them spin! Tap Next to find out their secret. 👉
Teeth that hold hands

Teeth that "hold hands" 🤝 Gear teeth fit into the gaps between the next gear's teeth. They mesh — like fingers from two hands locking together. That grip is what lets one gear turn another. Lock the teeth together 🔒
Which way does it turn?

They spin opposite ways 🔄 Here's a cool rule: when two gears mesh, they turn in opposite directions. If the left gear turns clockwise (the way a clock's hands move), the right gear must turn anti-clockwise. ↻ clockwise ❓ The blue-purple gear on the right will turn…? ↻ Clockwise ↺ Anti-clockwise
Big gear, small gear

Big gear, small gear 🐢🐇 A small gear has fewer teeth, so it has to spin fast to keep up with a big gear. The big gear turns slowly, the small one spins quickly. Drag the slider and watch! BIG (slow) small (fast) Turn the handle 🌀 Big gear spins: 0° · Small gear spins: 0° Notice the small gear's line whizzes around far more times. That's a gear ratio!
Speed or strength?

Choose: speed or strength? 💪 Gears let us trade one thing for another. Match each job to the right gear setup. Tap your answer! 🚴 A bicycle going up a steep hill — you want extra pushing power so it's not too hard to pedal. Big gear drives a small gear(more speed) Small gear drives a big gear(more strength) 🏎️ A race car on a flat track — you want lots of speed. Big gear drives a small gear(more speed) Small gear drives a big gear(more strength)
Build a gear train

Build a gear train 🚂 Line up three gears so all their teeth touch, and turning one gear turns them ALL. Tap the empty space to drop in the missing gear and connect the chain. 1 ＋ 3 Drop in gear 2 ⚙️ Did you notice? Gear 1 and gear 3 spin the same way, because gear 2 in the middle flips the direction twice!
Gears all around us

Gears all around you 🌍 Gears are hiding everywhere! Tap each card to guess what's inside. 🕐Clock 🚲Bicycle 🥚Egg whisk 🚗Toy crane Tap a card to reveal how gears help! 👆 Revealed: 0 / 4
You're a gear expert!

🎉⚙️🏆 You did it! You now know how gears work together: 🦷 Gear teeth mesh so one gear can push the next. 🔄 Meshing gears turn in opposite directions. 🐇 A small gear spins fast; a big gear spins slow. 💪 Gears trade speed for strength (or strength for speed). 🚂 In a gear train, turning one gear turns them all. Next time you spot a clock or a bicycle, you'll know there are clever gears working together inside! ⚙️✨ Great work, young engineer. 🌟

Frequently asked questions

What is a gear and how does it work?: A gear is a toothed wheel. When its teeth lock into the teeth of another gear, turning the first gear pushes the second one round, passing movement and force from one wheel to the next.
Why do two gears spin in opposite directions?: When two gears mesh directly, the pushing tooth of one drives the gap of the other from the outside. That means if one turns clockwise, the gear next to it is forced to turn anticlockwise.
Why does a small gear spin faster than a big gear?: A small gear has fewer teeth, so it must turn more times to match the larger gear's teeth as they mesh. The small gear spins quickly while the big gear turns slowly but with more force.
What is a gear train?: A gear train is three or more gears lined up so all their teeth touch. Turning any one gear makes the whole row turn together, letting machines send motion across a distance.
Where are gears used in everyday life?: Gears are inside clocks, bicycles, egg whisks, hand drills, toy cranes and car engines. They let machines trade speed for strength or change the direction of turning.

How Gears Work Together

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Frequently asked questions

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