I could imagine a spring system under a large building allowing it to move with the solar and lunar tides. Japan, of course, has some extreme earthquake suspension systems built into many of their buildings already. But, about how much would it produce?

Ok, the

diurnal change in gravity on Earth due to the sun and moon is about 2 µm/s

_{2}.

The (previous) World Trade Center Towers weighed somewhere on the order of 500,000,000 kg

So...

F = ma

m = 500,000,000 kg

a = 2 µm/s

_{2} = 2 x 10

^{-6} m/s

^{2} = 0.000002 m/s

^{2}So, F = ma = 500,000,000 kg * 0.000002 m/s

^{2} = 1000 kgm/s

^{2} = 1000 Newtons

1 newton = 0.2248 pounds

So, you end up with a difference of about 225 lbs, occurring twice a day.

Work, of course, = Force x Distance, with the distance being something pretty small.

Anyway, you would be much better off attaching a dynamo to a single bench press machine in the gym in the building.

Or, you could think of it as the force exerted by 1 or 2 people entering or leaving the building (which otherwise has an occupancy of thousands).