Happy New Year to everyone. I’m back from holidays now – a nice week in Tongariro National Park and then a few days at the beach in Bay of Plenty (hoping there are no sharks out there).
One of the disadvantages of living in NZ’s largest inland city is that it takes a special trip to get to the sea. It’s been absolutely ages since I’ve been swimming in something with a salty flavour. So it was very noticeable to me when I ventured into shark territory that I actually float in sea water. In the swimming pool I have to work (just a little) to keep afloat. If I stop moving I slowly head for the bottom, feet first (I’ve tried).
Humans have a density pretty close to that of water (i.e. 1 kg per litre). Mine is obviously ever so slightly greater than 1, so put me in fresh water and I slowly sink. Some other people would float (I’m sure I used to float when I was younger). But sea water has a density a little higher than fresh water (about 3% higher on average), on account of the dissolved salt. It’s not a great deal of difference numerically, but when you have a density very close to 1 it’s enough to have a noticeable effect. When I lie on my back and keep still in calm sea water I stay where I am. The dissolved salt is enough to keep me afloat.
Unfortunately it’s probably now going to be the freshwater variety of swimming for a while (more accurately, chlorinated water), but I hope to get over to Raglan before the summer is out.