What exactly is the function of a rubber duck?

by Andrew Irving (on Wednesday 2nd December 2015)*

Ah Harry Potter, where would we be without you?

weasley

And where would we be without water?  Well, stuck frankly.

You see, without water, waves would be quite conceptual.  They’d be `those invisible things light and sound have’.

Luckily those ripples of water can be found all over the place, especially at bath time!

Now if you keep an eye on your (obligatory) rubber duck as you slosh the bathwater, you’ll notice something: (s)he’s mimicking you.

ducktran

So slosh the water up and down – your duck bobs up and down.

Here, your sloshing generates waves which move from one end of the bath to the other. But your duck won’t follow – (s)he just oscillates on the same spot.

Why? Because waves transport energy, not matter.

All demonstrated by a rubber duck. Clever muggles.

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* This blog was based on the YouTube video entitled `Flow of energy not matter in transverse waves’ by MadDogScience (see also its twin video `Flow of energy not matter in longitudinal and transverse waves’).