re: harvesting energy

If we're talking about kids powering their own devices, I think the
way to go is to turn "work" into play. The merry go round/hard bar
swing would fit in this category.

So basically, let's look at activities where energy exerted is ambient
anyway? What I mean is that the energy is being used up by the kids
anyway, so why not tap into those. An example is to give them some
variant of those "dance straps" meant to power cellphones before they
go off to run and play during recess and lunch break.

One way to tap into this would be to create new playground
installation toys which can be used for harvesting energy.

Q: how much abuse can a kinetic energy harvester withstand? A soccer
of basketball has a lot of kinetic and impact energy bouncing around.
I'd imagine that's too much abuse though, and whatever harvesting
mechanism would break from the forces.

Would piezo work there?

I think I remember a concept where a dance floor would have piezo
harvesters and when people dance on the tiles, they light up?

Another problem is battery... how efficient and how much can a battery
really store from these small bursts of energy?

Sorry guys, I can't do math anymore since I got traumatized in
college, so would appreciate it if these were translated into
equation-less layman's terms.