Fancy a dip?
Now this has got be what science is all about. Take a 25m swimming pool. Fill it with syrup. Then see if you swim faster or slower in syrup than in water.
You might instictively think, “Well, of course you would go slower in syrup - it’s too thick!” But, being thicker, each stroke of your arm would propel you forwards further. So the answer? You go at roughly the same speed! When you increase the viscosity (”thickness”) of your liquid, the extra drag on your body is cancelled by the extra pull of your arms, and you can swim along at the same speed.
Of course, this isn’t completely true. The syrup was only twice as thick as water, and if it gets too thick then viscous forces dominate. (A nice thought experiment is to imagine that if the viscosity of the fluid didn’t matter, we could swim at the same speed in a bowl of jelly (=jello, for the Americans) right up until it set, when we would suddenly stop!)
And this really is a serious question - think of people trying to understand aerodynamics, particularly for different planets where the air has different densities. Or what about bacteria swimming through the human body (a lovely thought…)?
Just spare a thought for the poor guy who had to clean out the pool afterwards…