Swimming and physics

"So how's your swimming going?" asks a friend of mine over beers last night.

While I was on holiday in Greece recently, I'd posted a couple of progress reports to facebook about learning to swim. Having seen those status updates, my friend knew that I'd been taking lessons from boyfriend T.

"I don't find it easy," I reply, "but basically I can now swim for as long as I can hold my breath :-). Given that a few weeks ago I couldn't swim at all, I think that I'm making reasonable progress!"

"So you can't swim with your head above water at all?" asks my friend, surprised.

"No," I reply, "not yet anyway. I need to keep my head down in the water to make sure that I float!"

"Actually, while I was at the hotel in Mykonos," I continue, "I noticed that the other guests had various different swimming styles. I don't think that I'll ever be able to swim like some of them do."

"Why not?"

"Well, some of them are able to keep their entire head out of the water while they're swimming. I guess it's a type of breast stroke, but they never get their hair wet and they do it so slowly too, perhaps only one stroke a second. I admit that I don't sink now like I used to, but I only just float so I just couldn't keep my entire head dry!"

"I don't think people who swim like that are swimming properly," replies my friend, with a knowledgeable look on his face, "so don't worry. It doesn't matter if you're not able to do that."

"But don't you think that this relates to the basic physics?" I ask, pursuing the subject. "I mean, doesn't it means that people who can do that are much less dense than me? I'm sure that if I had been able to do that then I'd have learned to swim ages ago."

"Actually," I continue, "while I was on holiday, I bet boyfriend T that he couldn't swim like that, keeping his head out of the water the whole time."

"Why?" asks my friend, still chuckling to himself about the fact that I'd admitted to being 'dense'.

"Well he's quite a muscular guy, so I reckoned that means that he's also too dense to swim with his head out of the water the whole time."

"And were you right?"

"Actually it wasn't clear! The first day when he tried, he admitted to me that he couldn't do it. But a few days later he managed to do better, except that he was having to do about three strokes a second to keep his head dry, so I felt that that proved my point :-). Do you think a person's density affects their ability to swim?"

"I suppose it must have something to do with it," he replies, "but I reckon skill is much more important. It's probably 90% skill, and only 10% physics, something like that."

This morning, I did a bit of research using google and found (here) the following question with a couple of answers:

Question: Hi, I would just like to know the average density of a human being. Daphne, aged 16

Answer 1: Well, it's just about the same as that of water, because when you put the average human being in water, he just barely floats in it. Some people (me, for example) can sink or float depending on how much air they hold in their lungs, so their density can vary from just below to just above 1.0 g/cm^3. Grayce

Answer 2: Daphne, do you float in water? Some very muscular people don't. I hope that answers your question. Felix

So do very muscular people have trouble swimming? Or is my friend right after all, so that the physics only accounts for 10% of someone's swimming ability?

In some sense, posting this kind of question on my blog is a bit like 'Ask the audience' on Who wants to be a millionaire! It's not exactly reliable, but nonetheless it's always interesting to see other peoples views :-).

So if anyone has any thoughts on this, I'd be very interested to hear them!