How a Crookes radiometer works

A Crookes radiometer is driven by a thermal gas effect, and not "light pressure" as often thought. I demonstrate the radiometer in a vacuum chamber and explain its optimal running pressure.

[kurtschlarb]

Mister, this is the best, simple explanation of this phenomenon I have ever seen, heard, or read.
Old video. Hope you're still out there.

[johndedwards]

I’ve just watched this and practically jumped up when you said you might try to make a radiometer with larger blades. I’ll be looking for that right now, but if you haven’t *please* do!

Loved this! Subscribed.

[HorseJouster]

You should definitely make one with 1.5 cm vanes and then one with .5cm vanes and see if there is a linear link to the gas molecules. That'd be very interesting!

[captoshu]

Very interesting! This is the best example of describing what's going on I've found yet. Thank you for deep diving into it!

[horrorhotel]

How can one resist such temptations?

You truly are a man of iron will

[zakunknown]

I was told in science class in 2003 that this was due to light hitting the sides not heat. I remember being confused at the time of the direction it spun.

Good to know. thanks for the video!

[electronicsNmore]

These radiometers are neat. I vividly remember when I was a kid going to a planetarium and looking at one of these. Nice video!

[SimoWill]

So in the argument I had with my high-school science teacher 30 years ago, I was right. Huh. I wonder if I can find him to say 'told ya'.

[eCitizen]

This is very thorough and informative. Thank you for taking the time to give this a proper explanation.

[jfmc]

Wait wait wait!!!! You never ever explained how it moves Backwards when cold!!!

And you really skipped over how the "second " way it turned works!!

Thank you for the video but we NEED MORE!!!

Thanks!

[hkhkhnkhk]

The scientific term for the force is "Photophoretic force". Your observation is very interesting because in micro particles the force peaks when the mean-free-path of the gas is the same as the diameter of the particles. This force can be used to trap and guid particles which absorbs light.

[AllMiles]

Well done. Operation clearly explained. Very engaging by using a vacuum chamber and oscilloscope to collect data from sensor.

[clientesinformacoes]

I think you should switch the colors so we can have more data. It cold be related to the vibration of the atoms that can absorb kinetic energy from one place and releases to another, just like a sound levitation but in a form of radiation. The energy travels through the gas molecule in certain frequency, if there's no gas, the eneryt can not be transferred, if there are to much gas, it cancels each other out. Try with magnetic sheets, cover with black and white and see if works in a vacuum.

[tuopeeks]

Blown away with the freezer spray cooling even repeated that one at home to see it again. Did not expect that to work still thinking about it. 

[howardhiggins]

Always love your experiments.
I can remember hundreds of radiometers on a big table for sale, at Disneyland.

[jjeherrera]

So I had been fooled to believe all this time that it was radiation pressure. Now I understand why I couldn't understand it...because it couldn't be radiation pressure! Thanks for the clear clarification.

[dalenassar]

Did you know that at the first part of the video, many people can't tell which way the fins are turning?? I am one of those..it even appears to reverse directions at this straight-on view! I had to watch it 'start' turning to be sure.
Since I was a kid, a radiometer is one thing that I wanted...decades later, I finally put one in a microwave oven (with a water load).. It turned very fast at first, then there was a spark at the tip of the needle (blunting it due to the high EF build-up)...never worked again...gotta get another one one of these days!
GREAT VIDEO!

[EclecticBuddha]

I think I'm picking up what you're laying down but 
A: What info is given with the packaging? You just did a really cool experiment to find out info that I feel like the makers could easily include or even print onto the base. It's a learning tool for Pete's sake.
B: I am now angry at every science teacher I had that had one of these on the shelf (almost all of them) and never brought it up or just had it so we could look at the spinny thing and not bother them for awhile.

[THGD]

The first time I saw one of these I was told that the force was delivered by the photons.
Great video man.

[AdamBechtol]

Been watcing a few videos on this, glad to see you made one as I trust you on such matters the most.