Does centrifugal force result from the mass of the rest of the Universe, or from the mere presence of other matter in the Universe ( i.e. with the latter providing a remote frame of reference independent of its mass)?
Centrifugal force, as far as we’re concerned, has nothing to do with external mass. If you’re thrown into an empty universe with a ball attached to a string and you start swinging it over your head, you’re still going to feel a pull on your hand. Centrifugal force is a manifestation of inertia, if that’s the answer you’re looking for.
ahem
There is no such thing as centrifugal force. It’s centripetal force.
Or so my college physics teacher told me.
Well, centrifugal force is a result of analyzing a situation relative to a rotating reference frame. It’s often called an “inertial force” because it won’t appear if you analyze in a non-rotating reference frame.
Suppose you are standing on a real fast merry-go-round. You will feel an apparent centrifugal force. It is valid, by the principles of General Relativity, to analyze the situation by assuming that you are at rest and the universe is spinning around you. In that analysis, you will find a gravitational effect (that is indistinguishable from an acceleration, by the “equivalence principle” of General Relativity) that produces the “force” that you can feel.
See INERTIA THEORY - Paul Davies On The Meaning Of Mach’s Principle. Also see Is Centrifugal FOrce Real? and Is there such a thing as centrifugal force?.
jrf
Another way to look at the ball swinging at the end of the string is that it’s constantly accelerating. It may be revolving at a constant rate but the natural tendancy for an object in motion is to continue in a straight line. The force of the ball pulling away from the circular path is equal to the force of the string pulling on it just as the love you take is equal to the love you make.
Since nobody’s given the high school explanation of this yet, I will.
Take a ball being swung in a circle around a pivot point (“axis”… can we all say that?). Now peep this: the ball’s actual velocity at any given moment is tangential to the circle of revolution. What makes it move in a circle is the ball’s acceleration, which is always pulling the ball directly towards the centre of the circle.
The string doesn’t want to go to the centre of the circle any more than Earth wants to fall into the Sun. The pull on your hand is really the ball pulling against the string.
Now you say, “why doesn’t the Sun fall into Earth if they’re pulling on each other just as hard?”… the Sun is so massive that the force is relatively insignificant. However, there are binary star systems in which stars orbit one another.
Uh… any more questions before recess?
To expound a little more:
Centrigual force is also sometimes called a “fictitous force”. Ther is some disagreement over whether this term is valid. I side with the camp that says “you can feel it, it can appear to do work … therefore it exists”. Regardless of your philosophical postiion, it only appears in rotating reference frame and is meaningless in non-rotating reference frames.
The question of what would happen if we stood on a merry-go-round in an otherwise empty universe is interesting, but is obviously a tad difficult to test experimentally. Einstein’s original calculation of a “stationary” observer around whom the Universe rotates required mass in the rest of the universe. I think the final formulation does not require mass outside the observer, but I confess that I can’t say for sure. You can read some of Einstein’s words here and in the following page.
There are some theorists that think that the “virtual particles” predicted by Quantum Theory are involved in this somehow.
jrf
It’s a little off-topic, but …
Your statement may be misleading. The center of gravity of the Sun does move in response to the pulls of the planets. But the radius of the Sun’s “orbit” is much smaller than the radius of the Sun, so it’s common to ignore that orbit.
jrf