Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Is gravity-powered light possible?

Learn more physics!

Most recent answer: 04/10/2014
Q:
Hi, This link is to a winner of a 2013 Invention award from the magazine Popular Science. http://www.popsci.com/technology/article/2013-04/lighting-ballast-bulb?dom=PSC&loc=recent&lnk=10&con=IMG I know nothing about Physics but a colleague of mine assures me that this machine defies the laws of Physics and is simply impossible….. I however find it improbable that a mainstream Science magazine would judge and award a major prize to a machine which (my colleague assures me) is predicated upon a basic and glaring Physics mistake….and that such an entry would make it to the crowd-funding stage without anyone having noticed this supposedly basic error Please resolve this argument? Many thanks in advance Adam Contra
- Adam Contra (age 48)
Odessa, Ukraine
A:

Your friend is no doubt concerned about where the energy comes from to power this light. The energy is supplied via the muscles of whoever lifts up the rocks etc. to put in the bag. Then that gravitational potential energy is gradually converted to (mostly) electrical energy as the bag slowly falls, driving the generator. The LED does an efficient job of converting a good fraction of the energy to light. 

Your muscles get the energy from food or from stored body fat. Whether that's more convenient than carrying around some batteries depends completely on the situation. 

What surprises me is that the site says the device cost $300,000 to develop. Small electrical generators and LED lights are standard inexpensive commercial products. A bag, a pole, some pulleys and gears don't seem like they would cost all that much to develop. Maybe that cost includes manufacturing and distributing the first 7000 units, in which case it sounds about right.

Mike W.

 


(published on 04/10/2014)

Follow-up on this answer.