How Does It Work? Quiz

Answer: ABS releases and reapplies the pressure several times a second to stop the wheels locking. A locked wheel skids and you can no longer steer. Sensors monitor each wheel's speed; as soon as a wheel is about to lock, ABS briefly releases the pressure and then restores it, very quickly. The right reflex: keep the pedal firmly pressed, without pumping it.

Answer: The waves only penetrate a few centimetres; the centre then heats more slowly by conduction. Microwaves agitate water molecules, mainly in the outer layers. The turntable helps spread the energy, but nothing beats a minute or two of standing time and a stir halfway through.

Answer: The outer wheel travels further and must turn faster than the inner wheel. Without a differential, both driven wheels would turn at the same speed and the tyres would scrub in every bend. Its drawback: if one wheel spins on ice, it gets all the power. Hence the limited-slip differentials found on sports cars and 4x4s.

Answer: A radar or infrared sensor detects movement or presence in front of it. The radar spots anything moving towards it, while an infrared presence sensor stops the door closing on someone standing still in the doorway. That's why someone walking very slowly is sometimes ignored… until they wave.

Answer: The dynamic microphone. In a dynamic microphone, sound vibrates a diaphragm attached to a coil near a magnet: this movement produces a small electric current. A loudspeaker does the opposite. In fact, an earphone plugged into a mic input can pick up a voice.

Answer: Without relativistic correction, the position error would grow by about 10 km a day. GPS works out your position from the time taken by signals from several satellites. In orbit, weaker gravity and the satellites' speed shift their clocks by about 38 microseconds a day. That sounds tiny, but without correction the position would drift by kilometres every day.

Answer: The infrared radiation emitted by the surface it is aimed at. Every object emits infrared radiation, more intensely the hotter it is. The device picks it up and works out a surface temperature. Beware: shiny surfaces such as aluminium emit little and skew the reading.

Answer: A micro-resistor heats the ink in a flash; a vapour bubble pushes out a droplet. This is 'thermal' inkjet: thousands of nozzles each eject droplets of a few picolitres, thousands of times a second. Other manufacturers use a piezoelectric crystal that flexes to push the ink out, without heating it.

Answer: NFC works at very short range through magnetic coupling, which limits interception. NFC, derived from RFID, only works at about 4 cm: a deliberately tiny range that prevents accidental payments and makes eavesdropping from a distance harder. Phones usually add authentication by fingerprint or face.

Answer: It is the best compromise between efficiency, stability and cost. Two blades cause vibration and jerky running; more blades cost more and make the rotor heavier for little gain. According to Betz's law, a turbine can in any case only capture about 59% of the energy in the wind passing through it.