Question 1

What causes lightning?

Accepted Answer

A vast electrical discharge between regions of separated charge — and the honest position is that **how the charge separates in the first place is still not fully settled**, which surprises people about such a familiar phenomenon.

**How charge builds up.** Inside a thundercloud, strong updrafts carry water droplets, ice crystals and soft hail. The leading explanation involves **collisions between ice particles and graupel**, which transfer charge, with lighter ice crystals carrying positive charge upwards and heavier graupel carrying negative charge downwards. The result is a cloud with a positive top, a negative base, and frequently a small positive region beneath. **The details of the charge transfer remain an area of active research.**

**Why a discharge happens.** Air is an excellent insulator, so an enormous potential difference — many millions of volts — must accumulate before it breaks down. What triggers breakdown is itself debated, since measured field strengths in clouds are frequently lower than laboratory breakdown thresholds; cosmic ray interactions are one proposed explanation.

**The sequence of a strike**, which happens faster than the eye resolves:

**A stepped leader** descends from the cloud in branching jumps, creating an ionised channel.

**Upward streamers** rise from tall objects on the ground.

**Connection**, and then the **return stroke** — an extremely bright surge travelling **upward** through the established channel. The flash you see is the return stroke, moving from ground to cloud, which is the opposite of the intuitive picture.

**Multiple strokes** frequently follow down the same channel, which is the flickering.

**Why there is thunder.** The channel reaches around **30,000 kelvin**, several times the surface of the Sun, in microseconds. The air expands explosively, producing a shock wave that decays into sound. Distance in kilometres is roughly the delay in seconds divided by three.

**Why it strikes tall objects** — they shorten the gap and concentrate the field. **Lightning does strike the same place repeatedly**, which is exactly why tall structures have conductors.

Question 2

Why do clouds form, and why do they stay up?

Accepted Answer

Clouds form when air cools to the point where it can no longer hold its water vapour, and they stay up because the droplets are so small that air resistance almost entirely offsets their weight. Why

Question 3

What causes the northern lights?

Accepted Answer

Charged particles from the Sun colliding with gases in Earth's upper atmosphere, guided to the polar regions by the planet's magnetic field. The sequence: The Sun emits the solar wind — a continuous

Question 4

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 5

What causes rainbows, and why are they always curved?

Accepted Answer

Refraction, reflection and dispersion inside raindrops — and the curve is a consequence of geometry rather than of anything about the sky. What happens in a single drop: Light enters the drop and

Question 6

Why do we get goosebumps?

Accepted Answer

Because a tiny muscle at the base of each hair contracts and pulls the hair upright, tugging the surrounding skin into a bump. In humans it is a leftover reflex that no longer does much, but the

Question 7

Why does ice float on water?

Accepted Answer

Almost every substance is denser as a solid than as a liquid, because cooling slows molecules and lets them pack more tightly. Water is a notable exception, and the reason is the geometry of hydrogen

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