You are here:

# Physics/Basic Physics

Question
Hello Dr Nelson,
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&l

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

This is my colleague's critique:
..."Don't people study physics anymore? Won't work, do the energy math. You won't get anywhere near the power that a meager LED light needs. If you lift a mass of 10kg two meters above the ground you get a potential energy of mgh = 196.2 Joules. A led blub needs at least 2 watts (hyper-optimistic estimate), which means that this system can power that light for.... 98 seconds. Your energy lifting constantly the whole thing would be better spent winding up an ordinary crank light. And I'm not even considering the loss due to gear friction and energy conversion.
Gee, I'm so fed up with these would-be "engineers" putting up one stupid "concept-product" after another, without any regard of even basic physics...."

...and this was a proof offered in the Comments Section of the link which my colleague also says is incorrect:
..."E=mgh.
m=20 lb=9.072kg, g=9.81m/s^2(42.2ft/s^2), h=10ft=3.05m
E=271.44J
W(weight)=0.151 watts over 30 minutes(1800 sec)
multiply by the efficiencies: n(gears)~0.9 and n(alternator) ~0.8 (these are estimated)
W(light)=0.109 watts
A standard LED bulb pulls around 0.04-0.09 watts, so this is plenty for one or two bulbs..."

The second one is closer, though the article said even more mass.  Therefore it's not just correct, it's accidentally conservative.  I looked up the wikipedia (it's accurate) on LED power consumption, and yes they do draw tiny amounts of power, well within the range needed.  The device is just a generator powered by a falling weight, nothing new.  I think this device is optimized for arid parts of the world without power and camping or you could consider using water instead of rocks for a weight.  No biggie, but even ultra-high output LEDs only use 0.04-0.1W of power (the second argument got that right), not the 2W consumed by the bulb the first person claims.  LEDs use a quantum process, incandescent bulbs are >95% inefficient because of heat loss.  Therefore, with a small weight increase to the rated weight, the 0.152W (probably tuneable with the right gears), you could power an equivalent 3W bulb.  That's weak, but enough to see by.   "Other devices" are pretty much out unless you're willing to really work to power your iphone for a couple of seconds.  It's still far easier to use a small solar panel during the day to store energy in a battery, like yard lights.  They're already in stores everywhere for \$2/stake in sets of 24.  They could be easily modified by anyone with a soldering iron and some wire to bring the lightbulbs themselves indoors.  (I got that price from a set of 24 at rakuten.com for reference, quick google search.)

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.