Question 1

Why do we have fingerprints?

Accepted Answer

The traditional answer — that ridges improve grip by increasing friction — has been seriously challenged, and the current best explanation involves touch sensitivity and water.

The **grip hypothesis** assumed fingerprints work like tyre tread. Research complicated this. A 2009 study measuring friction between fingertips and smooth surfaces found that ridged skin actually produced **less** friction than flat skin against smooth materials, because the ridges reduce the contact area. That is the opposite of what the tyre analogy predicts.

Two better-supported explanations have emerged.

**Enhanced touch sensitivity.** The ridges amplify vibrations as a fingertip moves across a surface, and the spacing of the ridges appears tuned to the frequency range that a particular class of touch receptor — Pacinian corpuscles, sitting deeper in the skin — responds to best. In effect the ridges act as an amplifier that converts fine surface texture into a signal the nervous system can read. This would explain why humans can detect surface features on the scale of tens of nanometres.

**Water management.** On wet surfaces the ridges act as drainage channels, letting water escape from the contact area so the skin can make proper contact. This is related to why fingers **wrinkle** in water — a response now understood to be actively controlled by the nervous system rather than simple swelling, and which improves grip on wet objects.

Fingerprints form in the womb, influenced by the growth of the skin layers and the position of the foetus. Identical twins share DNA but not fingerprints, which is why they are useful for identification.

Koalas also have fingerprints almost indistinguishable from human ones.

Question 2

Why does soap work?

Accepted Answer

Because soap molecules have two ends that want incompatible things, and that split personality is what lets water carry away substances water cannot normally touch. The problem soap solves. Water is

Question 3

How do we see individual atoms?

Accepted Answer

Not with light — atoms are far smaller than the wavelength of visible light, so no optical microscope can ever resolve them. The images you have seen come from instruments that feel surfaces or use

Question 4

Why does metal feel colder than wood at the same temperature?

Accepted Answer

Your skin does not measure temperature. It measures how quickly heat is leaving or entering it. Metal and wood sitting in the same room are at the same temperature, but metal removes heat from your

Question 5

What is plate tectonics?

Accepted Answer

The theory that the Earth's outer shell is divided into rigid plates that move relative to one another over a weaker layer beneath — explaining earthquakes, volcanoes, mountain ranges and the

Question 6

Why do I get more static shocks in winter?

Accepted Answer

Because winter air is dry, and dry air lets electric charge build up instead of leaking away. Static builds through contact and separation. Walking across a carpet, pulling off a jumper or sliding

Question 7

Why does a bicycle stay upright when moving?

Accepted Answer

This turns out to be a genuinely subtle question, and the explanation most people were taught is largely wrong. The common answer — gyroscopic effect — holds that spinning wheels resist tipping.

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