Crookes Radiometer

Edit: I just came across it on ThinkGeek, and it has a great explanation about it:

http://www.thinkgeek.com/geektoys/science/9bec/

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I was walking around Stockholm and I came across a fantasy store, in the back was this little glass ball with 4 squares spinning inside. Fascinated, I asked the owner, and he told me about it. Called a Crookes Radiometer, he claims the ability to make it was lost when the inventor died, and someone had finally figured it out again a few years ago, though exactly how it works is a mystery. There are 2 thoughts on how it works, one with heat transfer and one about photons.

I have a little trouble believing the story, and I will be spending time looking up how it works, but in the mean time, here it is for you to see.

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Entertainment

Tags:

• Crookes
• Radiometer
• physics

[PANZER7910]

I think you guys confuse the term "heat". "Heat" is the measure of energy flow, not momentum transfer. The concept of heat cannot explain where comes the force to push the device. (although it actually increase temperature of the black blade)

Light particle carries momentum according to Einstein's energy equation.. It is the momentum transfer from photon that cause the device spin (remember Newton's Law).

[rhenretta]

@PANZER7910 I wasn't saying heat itself causes the momentum transfer, but the delta of temperature from the warm side to the slightly less warmer side. Since the few air particles that exist inside the partial vacuum move to the cooler area, as they do so they flow around the vane, and their momentum is transferred to the vane, causing the rotation. I don't believe the momentum comes from the photons colliding itself, but I could very well be wrong.

[PANZER7910]

@rhenretta @rhenretta @rhenretta I misunderstood the working principle before. "Thermal transpiration" can explain this phenomena.....

"the gas will flow through from the cooler to the hotter side"

[rhenretta]

@PANZER7910 Where did that quote come from? Gas flows from hot to cool, not the other way around. The warmer a gas, the higher the pressure, and the pressure equalizes my moving to the cooler area.

[61miroman]

Thermal transpiration is the the culprit. Black absorbs the heat from the photons neutrons much better than white. So we can say white repels and black attracts. The difference between the two is what makes it spin. So the photons create the heat? Very confussing I hope they can make electrical power plants with this concept.

[rhenretta]

@61miroman Yes, photons create heat. They are basically little packets of energy, and when they are absorbed that energy is transferred to the object which absorbed it. Since the black sides absorb more photons, it is slightly warmer on that side creating an area of higher pressure. The other side has an area of lower pressure. The higher pressure wants to move over to the low pressure, and hence the movement. It is very inefficient though, we are better off with solar power.

[PANZER7910]

@rhenretta wikipedia.>crook radiometer>explanation



[PANZER7910]

@PANZER7910 Sorry, I am giving a wrong concept...what I explain is for Nichols radiometer...not this one...

[TheDustFactory]

what are the vanes made of?

[CaptainCrossOver]

My teacher explained it to my in under 5 mins