Skipping stones like a boss

Vector addition is key to understanding the interaction of stone and water. Source: http://arxiv.org/pdf/physics/0210015v1.pdf
Vector addition is key to understanding the interaction of stone and water. Source: http://arxiv.org/pdf/physics/0210015v1.pdf

One of my favourite games as a youngster was to skip stones on water. I was really bad at it – and still I became a physicist, a rocket scientist even.

So, why does a stone skip on the water?

You can find answers here at Quora. It is basically about vectors and where they point. It often is.

It is also about the surface tension of the water reacting to the stone falling onto it. Newton’s third law tells you that the stone will experience an upward force due to pushing the water downwards. There is more to it, of course, like the angle at which one has to make the stone hit the surface of the water, rotational stability and the shape of the stone. I will not try to improve on what are excellent explanations of the whole thing. Click on the hyperlink above and read them.

But it just hit me the other day, when I put this out there on social media, that skipping stones is not all that different from rocket physics. Newton’s third law is behind rocket propulsion. You blow stuff out one way, the rocket goes the other. The rest is about stabilizing the object. With a rocket you use wings to make it rotate. The stone you try to give rotation when throwing it.

If you are into checking it out for yourself, you can follow the maths by reading this instructive arXiv-paper, which is also linked to in the excellent Quora-answers above. The similarities to rocket science are not superficial at all!

I should have known that this was rocket science, when I was a kid. My interest in the whole process would have increased immeasurably. I would have skipped that stone like a boss, of that I am sure.


12108755_1507250599599792_3692866167745201820_nAlexander is a physicist, teacher and science communicator who is currently working at the Norwegian Centre for Space-related Education at Andøya Space Center in Norway. Even though, in his case, work and play do overlap, the content on this webpage is entirely private. You can follow Alexander on Twitter, Facebook and Google +

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