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How doable (guess not) would it be to make a "gravity battery" ? A tiny but heavy balls are thrown from top and while passing thru thin channels they rotate som

How doable (guess not) would it be to make a "gravity battery" ? A tiny but heavy balls are thrown from top and while passing thru thin channels they rotate some sort of mini-dynamo that creates electricity. Once all balls are on the bottom, generated electricity is used to rotate the whole thing and start process anew. Anyone with a napkin can elaborate why this is not feasable?

system2 4y ago
No need napkins for it. Because of friction and other forces the dynamo does not generate enough energy to lift the balls back up and have extra to be stored for other uses. In short, you use more energy to lift them than produced. If anyone could invent such a device, the world hunger and money wouldn't be problems anymore and we would be traveling to the end of the universe already.
- minitoar 4y ago
  I’m pretty sure by “generated electricity” they mean from some other source.
kamilner 4y ago
The amount of energy from a 1 tonne mass dropping 1 meter is about 10,000J (https://www.wolframalpha.com/input?i=%281+tonne+*+9.82m%2Fs%5E2+*+1+meter%29 https://www.wolframalpha.com/input?i=%281+tonne+*+9.82m%2Fs%...) The amount of energy stored in a Tesla is about 100kWh or about 3.6e8J. You would need 36,660 tonnes suspended by a meter to store an equivalent amount of energy (or 1 tonne suspended 36.7km). https://www.wolframalpha.com/input?i=100kWh+%2F+%281+tonne+*+9.82m%2Fs%5E2+*+1+meter%29 https://www.wolframalpha.com/input?i=100kWh+%2F+%281+tonne+*...
- addaon 4y ago
  Or one Tesla Model S (~4600 lbs) suspended 17.6 km. With a range of ~400 miles, this means the storage-Tesla would have to drop ~0.027 units per unit travelled by the drive-Tesla, giving a "glide ratio" of ~36:1, which passes the sniff test on reasonableness.
danuker 4y ago
Switch the balls with water, and the channels with turbines, and you have discovered a hydroelectric reservoir, which is quite feasible, given that quite a few are already built. > Once all balls are on the bottom, generated electricity is used to rotate the whole thing and start process anew. If here, you mean part of the electricity generated by the flow, then it can't work because pumping it back up is subject to friction (in fact, generation from when it flows down is also subject to friction) and to mechanical/electrical conversion losses. On a 100% efficient system with no losses, you would get perpetual motion, but subtracting any energy from the system would make it slow or stop.
folmar 4y ago
The closest that you have in real life is pumped-storage hydroelectric power station.

system2 4y ago

No need napkins for it. Because of friction and other forces the dynamo does not generate enough energy to lift the balls back up and have extra to be stored for other uses. In short, you use more energy to lift them than produced. If anyone could invent such a device, the world hunger and money wouldn't be problems anymore and we would be traveling to the end of the universe already.

minitoar 4y ago
I’m pretty sure by “generated electricity” they mean from some other source.

kamilner 4y ago

The amount of energy from a 1 tonne mass dropping 1 meter is about 10,000J (https://www.wolframalpha.com/input?i=%281+tonne+*+9.82m%2Fs%5E2+*+1+meter%29 https://www.wolframalpha.com/input?i=%281+tonne+*+9.82m%2Fs%...) The amount of energy stored in a Tesla is about 100kWh or about 3.6e8J. You would need 36,660 tonnes suspended by a meter to store an equivalent amount of energy (or 1 tonne suspended 36.7km). https://www.wolframalpha.com/input?i=100kWh+%2F+%281+tonne+*+9.82m%2Fs%5E2+*+1+meter%29 https://www.wolframalpha.com/input?i=100kWh+%2F+%281+tonne+*...

addaon 4y ago
Or one Tesla Model S (~4600 lbs) suspended 17.6 km. With a range of ~400 miles, this means the storage-Tesla would have to drop ~0.027 units per unit travelled by the drive-Tesla, giving a "glide ratio" of ~36:1, which passes the sniff test on reasonableness.

danuker 4y ago

Switch the balls with water, and the channels with turbines, and you have discovered a hydroelectric reservoir, which is quite feasible, given that quite a few are already built. > Once all balls are on the bottom, generated electricity is used to rotate the whole thing and start process anew. If here, you mean part of the electricity generated by the flow, then it can't work because pumping it back up is subject to friction (in fact, generation from when it flows down is also subject to friction) and to mechanical/electrical conversion losses. On a 100% efficient system with no losses, you would get perpetual motion, but subtracting any energy from the system would make it slow or stop.

folmar 4y ago

The closest that you have in real life is pumped-storage hydroelectric power station.