女生小视频

rainy days rain drops on the window surface ; Shutterstock ID 724215220; purchase_order: -; job: -; client: -; other: -

Why does water never move in straight lines?

Readers explain that a water droplet is subject to many invisible forces that cause it to snake down a windowpane

Male nose close up bottom view - hair in the nostrils; Shutterstock ID 1895123341; purchase_order: -; job: -; client: -; other: -

I understand why we have two eyes and two ears 鈥� but why two nostrils?

an australopithecus, one of our ancestors; Shutterstock ID 790742188; purchase_order: -; job: -; client: -; other: -

When did humans first start to sing? Part 2

JAPAN. Tokyo. Bank near Tokyo Station. 2002.

This week鈥檚 new questions

Battle cruiser approaching light speed in an outer space wormhole, 3d digitally rendered illustration; Shutterstock ID 91289105; purchase_order: -; job: -; client: -; other: -

How long would it take to accelerate to 99 per cent light speed?

an australopithecus, one of our ancestors; Shutterstock ID 790742188; purchase_order: -; job: -; client: -; other: -

Is it known when humans or our ancestors first started to sing?

Lola the Cat, behind a window, London

This week鈥檚 new questions

P2H56B Weasel standing upright, Mustela nivalis, Germany

Why do many animals have white undersides?

PE5P96 Close up of two purple socks with yellow lemon detail, pegged to a washing line with two yellow clothes pegs, shot from below against a clear blue sky

Why do plastic clothes pegs fade and get brittle in the sun?

Outdoor Backpack with Water Bottle on the back of a girl, School, isolated Green background Nature. Education concept; Shutterstock ID 2038295597; purchase_order: -; job: -; client: -; other: -

Is it more efficient to cart water in a bottle or my stomach? Part 2

More readers wade into the debate on whether it is better to carry a container of water and drink when necessary or guzzle lots of fluid at once

This week鈥檚 new questions

How do two photons become quantum entangled 鈥� and can I do it at home?

Why does some music give us goosebumps?

When a spirit level is flat, what does that mean relative to Earth?