GravityLight: Generate light with gravity • Hacker News Board

Re: GravityLight: Generate light with gravity

#51

Post by mikepurvis » Fri, Jul 31, 2015, 8:24 PM UTC

dear wrote: post #47

mdturnerphys wrote: post #33

Earlier quoted context omitted.

If we're playing that game: - Human muscles get energy from food. - Food is or gets its energy from plants. - Plants get energy from the Sun. - The Sun's energy comes from gravity-forced fusion. So gravity :)

So by your logic fossil fuel is solar energy.

It is, it's just massively time-shifted.

It's interesting to put that in perspective: the pyramids were built out of solar energy by way of muscle. Skyscrapers are built out of solar energy mostly by way of diesel fuel.

Re: GravityLight: Generate light with gravity

#52

Post by daenz » Fri, Jul 31, 2015, 8:26 PM UTC

mabbo wrote: post #8

There's a lot of reasons why this is cool, but I'm skeptical about it's aims to get rid of kerosene lamps. Kerosene lamps are made with garbage. They can be replaced in minutes if there's a problem. Fuel costs are high, yes, but capital costs and maintenance are low. Those matter. To really make this a long term win, you need to make it indestructible and easy to repair with on-hand parts. I hope they can do that.

> To really make this a long term win, you need to make it indestructible and easy to repair with on-hand parts.

That was the first thing I looked for. The materials, at least from this image, look plastic and very custom made. http://static1.squarespace.com/static/552aca94e4b0c75f5b87b0... If these parts get brittle and break/crack, how are they repaired?

Re: GravityLight: Generate light with gravity

#53

Post by ajuc » Fri, Jul 31, 2015, 8:28 PM UTC

brianpan wrote: post #46

ajuc wrote: post #37

Earlier quoted context omitted.

Good point, but it's not the end. Fusion uses up energy put there by the Big Bang :)

The Big Bang came from....gravity?

Is this the science consensus? I thought it's one of competing unconfirmed theories?

Re: GravityLight: Generate light with gravity

#54

Post by biot » Fri, Jul 31, 2015, 8:30 PM UTC

Perhaps a bit of a novelty given the rechargeable battery argument others have mentioned. I imagine distributing a bunch of these with batteries and having a central dynamo-powered recharging station that gets shared throughout a community would be even more practical.

The first thing that came to mind when I saw that it lasts 20 minutes would be to use it as a pomodoro timer. Code for 20 minutes, then be forced to take a break, stand up, lift the weight, etc. You get a micro-workout as a small bonus. Again, it's a novelty but sort of a cool one at that.

Re: GravityLight: Generate light with gravity

#55

Post by aidenn0 » Fri, Jul 31, 2015, 8:35 PM UTC

fla wrote: post #38

Vexs wrote: post #18

Earlier quoted context omitted.

Might be fun to make an electric clock that uses gravity, go full circle.

Rotor systems like in some automatic watches produce very little energy. Even at 100% efficiency it wouldn't be able to sustain an electronic circuit. Edit: I was wrong. See below.

My automatic watch contains an electronic circuit, so I'm not sure what your point is.

Re: GravityLight: Generate light with gravity

#56

Post by rcthompson » Fri, Jul 31, 2015, 8:35 PM UTC

mdturnerphys wrote: post #33

ajuc wrote: post #24

Nitpick, I know, but: it's not powered by gravity it's powered by human muscles, so in the end - by food.

If we're playing that game: - Human muscles get energy from food. - Food is or gets its energy from plants. - Plants get energy from the Sun. - The Sun's energy comes from gravity-forced fusion. So gravity :)

Stars are the original GravityLight.

Re: GravityLight: Generate light with gravity

#57

Post by benihana » Fri, Jul 31, 2015, 8:44 PM UTC

dear wrote: post #47

mdturnerphys wrote: post #33

Earlier quoted context omitted.

If we're playing that game: - Human muscles get energy from food. - Food is or gets its energy from plants. - Plants get energy from the Sun. - The Sun's energy comes from gravity-forced fusion. So gravity :)

So by your logic fossil fuel is solar energy.

It is. Except for geothermal energy brought on by radioactive decay, all energy on earth originally comes from the sun. Fossil fuel is sunlight that was absorbed by plants which then either decomposed into fuel over millions of years, or were eaten by animals which later decomposed into fuel over millions of years. Our cars are powered by very old, stored sunlight.

Re: GravityLight: Generate light with gravity

#58

Post by ris » Fri, Jul 31, 2015, 8:45 PM UTC

I implore people to support something far more practical like http://www.solar-aid.org/ than this.

Solar lights are many times more thermodynamically efficient, cheaper to make, smaller and much more robust (no moving parts!).

This "lifting weights" thing is a silly gimmick. A lifted weight stores a miniscule amount of energy compared to a battery that's been charged by the sun.

Re: GravityLight: Generate light with gravity

#59

Post by nine_k » Fri, Jul 31, 2015, 8:48 PM UTC

achr2 wrote: post #27

Years ago there was a similar 'potential energy to electricity' buzz and I was initially quite excited. Then I did the math on how much energy is actually available (even at 100% efficiency) from such a scheme. Spoiler - it's minuscule. E = mass x 9.81 x height So a 10kg mass at 2 meters can (@ 100% efficiency) provide 196 joules of energy. A modern cell phone battery has about 25000 joules. To charge said phone woul…

A kerosene lamp probably converts ~2-3% of its energy into the light; I don't think they use catalytic burners.

Dynamos and LEDs are reasonably efficient in comparison, and also not fire-prone.

Re: GravityLight: Generate light with gravity

#60

Post by lyschoening » Fri, Jul 31, 2015, 8:51 PM UTC

achr2 wrote: post #27

Years ago there was a similar 'potential energy to electricity' buzz and I was initially quite excited. Then I did the math on how much energy is actually available (even at 100% efficiency) from such a scheme. Spoiler - it's minuscule. E = mass x 9.81 x height So a 10kg mass at 2 meters can (@ 100% efficiency) provide 196 joules of energy. A modern cell phone battery has about 25000 joules. To charge said phone woul…

The key here is that this method does not require a battery. In practice though I am skeptical that this contraption would live much longer than a rechargeable battery combined with something more versatile such as a hand crank.