Science Questions

What would happen if you covered a swimmer with a hydrophobic substance?

Tue, 22nd Mar 2016

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Question

Luke Pearson asked:

Hi guys,

Great podcast! I was wondering what would happen if you covered a swimmer with a hydrophobic substance? Would they go quicker or slower?

Thanks!

Luke

 

 

Answer

We put Luke's question to chemist Ben Pilgrim... View from the starting block of a competition swimming pool.

Ben - Firstly Iíll just recap what a hydrophobic substance is.  Hydro obviously refers to water, phobic means dislike, so a hydrophobic substance is something that doesnít like water such as oil which wonít mix with water and will sit on the surface of water.  If we think about trying to move quickly through water, the main thing that stops that is drag.  Thatís the problem moving through any fluid at speed; itís how quickly you make your way through the fluid and this is actually is a very interesting question.  If you think back a few years ago you might have seen a number of swimmers wearing these full body suits which were subsequently bannedÖ

Chris - They were called the sharkskin suit, werenít they?

Ben - And these suits did a number of things.  One they sort of smoothed off the body to reduce little holes and things like that which might cause turbulence in the flow, but they also were coated in certain sorts of substances that trapped small amounts of air near to the surface and meant the water flowed over the swimmer much more quickly.

Chris - Did they work?

Ben - Did they work.  Yes, they were reckoned to produce about a 2% increase in speed and a lot of world records were broken.  However, this was then deemed that this was slightly unfair and so they were subsequently banned and limited in size.  So to go back to the question, the main thing with going fast is drag.  If you can have a hydrophobic substance that repels water, this can make a small increase, but the main thing is just to do with the shape at which the body is that moves through water.

Chris - And so, therefore, if you streamline your body but then you add something that repels water from your skin, it stops the water sticking to your skin so much, so you should go a bit faster.

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"I was wondering what would happen if you covered a swimmer with a hydrophobic substance? Would they go quicker or  slower?"
They do
http://marathonswimmers.org/forum/discussion/563/channel-grease/p1
so  I guess it's quicker- or at least more comfortable. Bored chemist, Mon, 7th Mar 2016

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