Why Do Spinning Liquid Mirrors Assume a Parabolic Shape?

AI Thread Summary
Liquid mirrors take on a parabolic shape due to the balance of gravitational and centrifugal forces during uniform angular motion. Centrifugal force, which increases with the square of the distance from the center, pushes the liquid outward along the x-axis, while gravity pulls it down along the y-axis. This unique interaction results in a surface where every point is equidistant from a focal point and a directrix, defining the parabolic shape. The discussion highlights the significance of these forces in determining the mirror's geometry. Understanding this principle is crucial for applications in optics and astronomy.
freemind
One simple question: why do liquid mirrors assume a parabolic shape when subject to uniform angular motion? (I mean, why not circular, or some other reasonably curved shape?)
 
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Think in terms of the definition of a parabola - the path followed by a plot of points equidistant from a point and a plane. You have two forces in play with a spinning liquid, gravity and centrifugal force. Centrifugal force pushes the liquid along the x - axis, gravity attracts the liquid along the y - axis. The centrifugal force component increases with the square of the distance from the center whereas the gravitational force component remains constant.
 
Wow, that makes so much sense! Thanks a lot Chronos. :smile:
 
Thread 'Question about pressure of a liquid'
I am looking at pressure in liquids and I am testing my idea. The vertical tube is 100m, the contraption is filled with water. The vertical tube is very thin(maybe 1mm^2 cross section). The area of the base is ~100m^2. Will he top half be launched in the air if suddenly it cracked?- assuming its light enough. I want to test my idea that if I had a thin long ruber tube that I lifted up, then the pressure at "red lines" will be high and that the $force = pressure * area$ would be massive...
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