It’s surprising what scientific principles are illustrated when taking a shower. Here are three that I have observed recently:
Do you remember those 1980s showers that were fed (via the hot water cylinder) from the cold water cistern in the roof? The cold water storage tank was only a few feet above the shower, so there was insufficient water pressure to give a decent flow at the shower.
Potential energy
This is Potential energy, where the height of the water tank determines the pressure of water at the shower. A slightly better shower could be achieved by squatting down, and so increasing the height difference – however this was not a very comfortable position to stay in for long.
I have one of those electric showers that heats the water as it flows through. The temperature control adjusts the water flow. The faster the water flows, the cooler the shower. Increasing the temperature means decreasing the water flow and vice-versa.
Pareto efficiency
Sometimes an acceptable shower becomes a compromise: I can have more water but lower temperature, or higher temperature but less water. This is an economic principle called Pareto efficiency which roughly means “you can’t make one thing better without making something else worse”. And yes, economics is a science – a social science.
Venturi effect
And finally, have you ever had one of those showers where the shower curtain is intent on wrapping itself around you? This is the Venturi effect. In a nutshell, the water in the shower hose is under pressure – there is lots of water compressed into a small space. As the water emerges from the shower head it spreads out into the area of the shower spray and the pressure drops. Consequently, the air pressure inside the shower curtain is lower than outside, and the curtain is sucked in.
To solve this problem, move the curtain rail down the wall a bit so that there is a gap between the top of the curtain and the ceiling. Now the pressures can equalise and the curtain stays where it is.
Right. People are hammering on the bathroom door. I think I’ve been in the shower for quite long enough now.
Last time you published your interpretation of Queue Theory in Table Hogging, my father-in-law had a rather different view of your interpretation and I was dragged into a strange conversation with him. Now you have new interpretation on 3 more scientific theories (while taking a shower) and I’ve started to get worried. I have no idea how right you are, but I do know there are keen scientists reading this blog.
Mine is “science for laymen”. It may not be entirely accurate, but the general gist is there – and hopefully sufficient for non-scientists to understand.
If you think your science is for ‘layman’, you’ll need to work a bit harder! Make it “science for dummies” next time!
I think the “xxx for dummies” title has already been taken – though as you can’t copyright the title of a work maybe I would be OK.
A couple of years ago I had to give a short presentation as part of a teaching qualification. I chose to do something based on economics. I started my talk by drawing a large bumpy shape on the board, then added a small dot to illustrate what a miniscule amount of all economic theory I would be covering. As I turned back from the board I remarked “and if you think that that diagram looks like a pile of horse poo, that’s because a large amount of economic theory is horse poo.”
I think the shower curtain effect is because the falling droplets of water drag some air with them. The air begins to move down and moving air has a lower pressure than static air.
Re: The Venturi effect. There is also a difference between laminar and turbulent flow. Turbulent flow has a much wider boundary layer (that is, the interface between the falling water and the surrounding air) and will draw in more air than laminar flow. If you steadily increase the water pressure, the water from the shower will stay laminar. Turn the tap too much, or bump the shower head, and it will become turbulent and suck the curtain in.
Is a power shower less environmentally friendly than an ordinary electric shower because of the energy and volume of water used? Or is it a more satisfying (and therefore shorter) shower, so there is no difference?
It may be a more effective shower, so people can get the same cleaning effect in a shorter period. However, my experience is that it is so satisfying that people stay in for longer as it is such a pleasant experience!
I think that you can get (though not sure where from) shower heads that give a power-shower experience, without the need for a pump. They use the venturi effect to suck more air into the shower head as the water flows through. I’ve never seen one of these in action, or heard of anyone who has – so if you have, do they work?
The water in the centre of the spray is hotter than that on the outside – this is because the jets in the centre are insulated by those on the outside.