Question 1

Why do mirrors reverse left and right but not up and down?

Accepted Answer

They do not. A mirror reverses neither — it reverses front and back, along the axis pointing into the glass. Everything else is an artefact of how you describe what you are seeing.

Consider what a mirror actually does to a point in space. Your nose, closest to the glass, appears closest in the reflection. The back of your head, furthest away, appears furthest. Left stays on the left side of the room and right stays on the right; up stays up. The only coordinate that flips is depth. A mirror image is the original with one axis inverted, which is why it cannot be rotated to match the original — the same reason a left glove cannot be turned into a right glove.

The confusion comes from the words. "Left" and "right" are defined relative to the body they describe, whereas "up" is defined by gravity and stays fixed no matter which way you turn. When you look at your reflection, you unconsciously imagine yourself turning around to face the other way. That imagined rotation is what swaps left and right, and you attribute it to the mirror.

Two demonstrations settle it. Lie on your side facing a mirror: the reflection now appears to swap head and feet, not hands — because you have changed which axis your body description is aligned with. Or hold up printed text: the letters are reversed left to right only because you rotated the page to face the glass. Hold the page facing you and read it through the back, and it is not reversed at all.

The mirror behaves consistently. It is our habit of describing reflections as rotated copies of ourselves that introduces the apparent asymmetry.

Question 2

Why does the Moon always show us the same face?

Accepted Answer

Because the Moon is tidally locked to Earth: it rotates on its axis exactly once for every orbit it completes. The two periods are synchronised, so the same hemisphere always faces us. A common

Question 3

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.

Question 4

Why does the moon look bigger near the horizon?

Accepted Answer

It does not actually get bigger. The moon's angular size when it is low is essentially identical to when it is high, and if anything it is marginally smaller near the horizon, because you are

Question 5

Does water really swirl the other way in the southern hemisphere?

Accepted Answer

Not in your sink, no. The Coriolis effect is real and genuinely does act in opposite directions in the two hemispheres — but it is far too weak to determine which way a basin drains. What the

Question 6

Why can't we feel the Earth moving?

Accepted Answer

Because you feel acceleration, not speed — and the Earth's motion is almost perfectly steady. The speeds involved are enormous. At the equator, Earth's rotation carries you at roughly 1,670 km/h. Its

Question 7

Why does sound travel further at night?

Accepted Answer

Because of how temperature is layered in the air, not because the night is quieter — although that helps you notice it. Sound bends toward regions where it travels more slowly, and it travels more

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