Gear playground, pendulum calculator and the quiz
Try the numbers, then test yourself. Every answer comes with its source.
How to play. Pick an answer and the fact behind it appears, with a link to where it comes from. Without JavaScript, open “Show the answer” under each question.
The gear playground
Choose the teeth on each gear. The orange one drives. Watch which turns faster, and read off the speed and force.
Move a slider to see the result.
Our own arithmetic from the gear rule Britannica: speed ratio = driven teeth ÷ driving teeth, and the turning force goes up by the same ratio (ignoring friction).
The pendulum calculator
Choose a length and see how long one swing takes. The drawing swings at the real speed.
Move the slider to see the result.
Our own arithmetic from T = 2π√(L/g) Britannica, for one swing from side to side (half the full period), with g = 9.81 m/s², ignoring friction and wide swings. A pendulum of about 99 cm beats seconds Britannica.
The clockwork quiz
1 What does a clock’s escapement do?
Show the answer
Lets the gears move on in small, controlled steps. An escapement lets motion happen in controlled steps. Britannica In a clock or watch it controls how energy passes from the power source to the counting mechanism. Britannica
2 A 10-tooth pinion drives a 20-tooth wheel. The wheel turns…
Show the answer
Half as fast, with twice the force. A driven gear with twice the pinion’s teeth turns with twice the force at half the speed. Britannica
3 What is the small gear of a pair called?
Show the answer
The pinion. The smaller gear of a pair is called the pinion. Britannica
4 About how long is a pendulum that takes one second per swing?
Show the answer
About 99 cm. A pendulum that takes one second per swing is about 39 inches (990 mm) long. Britannica
5 Make a pendulum’s bob heavier, keeping its length the same. Its swing time…
Show the answer
Stays the same. A heavier bob does not change the period, as long as the length stays the same. Britannica
6 Who made the first pendulum clock, in 1656?
Show the answer
Christiaan Huygens. Christiaan Huygens made the first pendulum clock in 1656. NIST
7 Which gearing drives the hour hand from the minute hand?
Show the answer
The motion work, 12 to 1. A simple 12-to-1 gearing, the motion work, drives the hour hand from the minute hand. Britannica
8 What did the fusee do?
Show the answer
Kept a watch’s mainspring pulling evenly. The fix was the fusee: a cone-shaped, grooved pulley linked to the spring barrel by gut, later a chain. Britannica Fully wound, the chain pulls on the narrow end of the cone; as the spring runs down it pulls on a wider part, so the leverage grows and the force stays almost even. Britannica
9 How many times a second does Harrison’s H4 tick?
Show the answer
Five times. H4 ticks five times a second: its big balance beats faster and swings wider than a normal watch’s. RMG
10 How many gear wheels did X-rays find in the Antikythera mechanism fragments?
Show the answer
30. X-ray images showed 30 gear wheels inside the fragments. Britannica
11 The oldest surviving clock in England, from 1386, is at…
Show the answer
Salisbury Cathedral. The oldest surviving clock in England is at Salisbury Cathedral, from 1386. Britannica
12 A worm gear can work with as few as…
Show the answer
One tooth. Because a worm is basically a screw it can have just one tooth, which makes a worm and gear good for a big speed change in one step. Britannica
Myth or fact?
Eight statements. Some are true, some are myths.
1 Galileo built the first working pendulum clock.
2 A heavier pendulum bob makes a clock run slower.
Show the answer
Myth. A heavier bob does not change the period, as long as the length stays the same. Britannica
3 The escapement is what makes a clock tick.
Show the answer
Fact. The escapement is what makes the tick-tock of a weight-driven clock. Britannica
4 Big Ben’s clock uses an escapement invented by Edmund Beckett, later Lord Grimthorpe.
Show the answer
Fact. Edmund Beckett, later Lord Grimthorpe, invented the double three-legged gravity escapement for the great clock at Westminster, now known as Big Ben, installed in 1859. Britannica
5 Every source agrees Harrison won the full longitude prize from the Board.
Show the answer
Myth. NIST says that by 1761 it had won the British government’s 1714 prize. NIST Royal Museums Greenwich says the Board recommended only half the reward in 1765, the rest to wait until other makers could build similar timekeepers. RMG Harrison was finally rewarded by Parliament, not by the Board of Longitude, and never got all he felt he was owed. RMG
6 A gear with more teeth, driven by a small pinion, turns more slowly but more strongly.
Show the answer
Fact. If the small pinion drives a bigger gear, the pair slows the motion down and boosts the turning force; drive it the other way and it speeds up but turns more weakly. Britannica
7 Medieval tower clocks kept time to within a few seconds a day.
Show the answer
Myth. These early clocks may have been out by as much as half an hour a day. Britannica
8 Quartz clocks beat pendulum clocks partly because they have no gears or escapements disturbing their vibration.
Show the answer
Fact. Quartz clocks beat pendulums because they have no gears or escapements to upset their steady vibration. NIST