It is inside a glass sphere with a glass tube that comes down outside the sphere and goes up to the center of the sphere. On the tip of the tubes top a cone sits on it with 4 arms that have one card on it. One side of the card is dark colored and the other side is white. When you but this thing in the sun it spins slowly. Why?
-My only guess is the heat from the sun is held on the dark side of the card and some how releases energy to move.
2006-09-15 12:32:22 · 9 answers · asked by GroundZERO 63 2 in Science & Mathematics ➔ Physics
You're asking how a Radiometer works, right?
I cribbed this information from "Howstuffworks" and here is the discription! :)- good luck
A Crookes' radiometer has four vanes suspended inside a glass bulb as you've described. Inside the bulb, there is a good vacuum. When you shine a light on the vanes in the radiometer, they spin -- in bright sunlight, they can spin at several thousand rotations per minute!
The vacuum is important to the radiometer's success. If there is no vacuum (that is, if the bulb is full of air), the vanes do not spin because there is too much drag. If there is a near-perfect vacuum, the vanes do not spin unless they are held in a frictionless way. If the vanes have a frictionless support and the vacuum is complete, then photons bouncing off the silver side of the vanes push the vanes, causing them to rotate. However, this force is exceedingly small.
If there is a good but incomplete vacuum, then a different effect called thermal transpiration occurs along the edges of the vanes, as described on this page. The effect looks as though the light is pushing against the black faces. The black side of the vane moves away from the light.
2006-09-15 12:37:38 · answer #1 · answered by Anonymous · 2⤊ 0⤋
It's a "Crooke's radiometer"... the sphere is partially evacuated to minimise air resistance (note that it won't work if you take all the air out...) and the bearing has to be very good!
Any kind of radiation that penetrates the glass will make it move, but infra-red (heat) is good... The dark sides of the blades absorb more radiant energy than the silver side, making them warmer... the gas molecules in the sphere's low-pressure atmosphere are heated on contact with the dark blades, and become more "active" than those on the silver side, which is cooler.
Thus, there is a difference in pressure between the dark and silver side, tending to push the blade away from the energy source.... in this case, around and around...
The "pressure of light" theory was postulated by Crooke himself, and disproved some time ago.
2006-09-15 12:48:42 · answer #2 · answered by IanP 6 · 0⤊ 0⤋
The thing is called a Radiometer.
What makes it turn is the very small remaining air. The dark sides absorb light and heat up, the light sides heat up less. The remaining air gets more excited near the dark sides and pushes them away, the air near the colder light sides pushes them less. So the radiometer turns, pushed by the dark sides.
If the movement was caused by the momentum from the photons (the particles of light), then the white or mirrored sides should receive more energy because they would be reflecting the photons, not just absorbing them. And the radiometer would turn the other way.
Just one comment: you say "slowly". A good radiometer, resting on a flat surface, in good sunlight, will turn very fast. Maybe yours has a problem?
Hope this helps
a
2006-09-15 12:54:50 · answer #3 · answered by AntoineBachmann 5 · 0⤊ 0⤋
The dark surfaces absorb the light and the mirrored ones reflect it, the push and pull of the two sides create the rotary movement, almost like a windmill, but based on photon pressure. The brighter the light the faster the motion!
The inside of the glass bulb has a vacuum in it. There is NO air movement.
2006-09-15 12:34:55 · answer #4 · answered by Anonymous · 0⤊ 0⤋
This is a famous experiment of the Russian scientist Lebedev that is proving that the mass of Photon of Light is not equal to zero: Photon absorbed on a dark sides and reflected from the light ones thus creating a difference of pressure on the lever that connected them. Difference of forces = momentum that rotates this mill. (There is a vacuum inside the sphere).
2006-09-15 12:47:46 · answer #5 · answered by Thinker 4 · 0⤊ 0⤋
The action of changing light to heat releases energy, propelling the dark side of the card.
2006-09-15 12:35:11 · answer #6 · answered by Pancakes 7 · 0⤊ 1⤋
Actually, just the opposite. The white reflects the photons and it is this energy, imparted when they bounce off that keeps the vanes in motion.
The dark side ABSORBS the energy.
2006-09-15 12:38:12 · answer #7 · answered by Vince M 7 · 0⤊ 0⤋
the cards are at a slight angle so rising heat pushes them sideways
2006-09-15 12:34:39 · answer #8 · answered by dicanus1 2 · 1⤊ 2⤋
idk, but if anyones 14-16 then messenger me
<33
2006-09-15 12:39:07 · answer #9 · answered by ♥Cree♥ 2 · 0⤊ 0⤋