91É«ÇéƬ

At the recent Commonwealth Games, I was struck by how many runners with long hair had tied it in a ponytail. When fractions of a second can decide a race, surely looser hair is a drag?

Helen Read,

Farnham Common, Buckinghamshire, UK

What happens to a photon after it hits the retina of my eye?

Adam Eri,

Vienna, Austria

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