An idea for gyms - use friction to heat water for hot drinks.
I propose a machine that uses human power (hand crank, foot pedal etc) to turn two discs of metal that are rubbing against each other in opposite directions. Something like a car disc brake or some other friction arrangement would do the job as well. The friction heats up those discs and a cupful of water is circulated through channels in the discs. The water is heated by the hot discs. Once hot enough, the water will get to boiling temperature and is drained to make a cup of hot tea or coffee. You will really have earned it!
This would also be a nice demonstration of human energy expenditure - you can actually feel/measure the energy that you have put into the device.
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How about this spin... you need to generate enough hot water to take a shower. Kind of like paying for a car wash at the pump. Enter your code at the shower and you get the minutes of hot water you earned. This would save some water too. If you don't shower, bank your minutes for free smoothie ingredients ...tht you can mix together with the bike powered blender.
Wouldn't cycling water for consumption through metal discs result in tiny metal particles in your drinking water? You'd need to isolate the heat fluid from the potable water source.
Probably you'd be better to pump it repeatedly (closed-loop) with a Tesla disk-pump which has no metal-to-metal contact, only the adhesion of the viscous liquid to multiple metal disks transmits the energy.
http://www.animatedsoftware.com/pumpglos/teslapum.htm
This way you would have less chance of getting metal in your water than the two-disks. Also adjustment of the friction could be easily done by varying the spacing of the Tesla disks, say with a knob.
Mostly when I get done exercising, I'm not looking for a hot-drink, though. You'll have to make a way to radiate or dump this hot-water for people like me.
Also, your machines will be better if they're connected to the water supply to replenish their own cold water before exercising--otherwise it would be a pain to always be filling a machine before you exercise.
Thanks for the comments. I anticipated putting the water in separate channels or tubes on the outside of the discs, not in between them, so no metal shavings would get in. That Tesla disk pump looks very clever - thanks for the link.I guess my primary idea with this was to make some hot water, not to exercise but I take the point that you'd probably not want a hot drink after a gym workout!
That's a cool idea!You have to think of the most efficient way of transmitting the enegry of your body into hot water. I thought of a heat-generator, but I've no idea if it's not too inefective.