Re: Rain and the laws of physics
- From: "Bob Myers" <nospamplease@xxxxxxxxxxxxxxx>
- Date: Sun, 6 Jul 2008 19:51:35 -0600
"Twibil" <jose.noway6@xxxxxxxxx> wrote in message
news:e7c78536-6aa7-4ea8-8937-d52916569abe@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 5, 5:56 pm, "David T. Ashley" <d...@xxxxxxxx> wrote:
Strictly speaking, if the speed of the bike is constant, the edge of the
wheel is accelerating towards the axle at all times.
Uh, no. It is revolving *around* the axle. The solid structure of the
wheel is all that keeps the edges from moving *away* from the axle,
not *towards* it.
Right, which means the solid structure of the wheel is
pulling the "edges" toward the center, right? Hence - it IS
correct to say the the edge of the wheel is constantly accelerating
toward the center when the wheel is rotating. David's right, and
this is basic physics. "Centrifugal force" is an illusion; the acceleration
is toward the center, and *inertia* is what makes it feel (to someone
at the edge of a rotating wheel) like there's a "push" outwards.
The earth goes around the sun, and the only force involved is a
gravitational force directed toward the sun.
Oh dear. If the only force involoved was gravity, we would promptly
fall into the sun; thereby solving the middle eastern problem once and
for all.
In fact, the force of the Earth's mass and velocity balance out the
Earth and Sun's combined gravity. (They each attract the other.)
Sorry, again David is exactly right. Mass and velocity together
are *momentum*, not a "force" per se. There is no force being
applied to or by the Earth which moves it forward or outward;
it is moving forward at a *constant* speed (since there's essentially
nothing in the vacuum of space to slow it down). The gravitational
attraction between the Earth and the Sun accelerate the Earth
inward (i.e., it is constantly "falling" toward the sun); it's simply that
the acceleration inward due to the force of gravity is balanced by
the forward velocity, such that the distance from the Sun remains
basically constant (well, yes, the orbit is actually an ellipse, not a
circle, but for purposes of visualization we can ignore that for now).
In other words, the Earth (or any other body in orbit) winds up
"falling around" the Sun. THAT'S what's called an "orbit."
I believe the physicists also claim that the acceleration required
(toward
the center) to hold a circular path is (V**2)/R.
Get a grip! A wheel is not in orbit around it's axle.
No, but that formula DOES give the acceleration as seen
at any point at the edge of a rotating wheel of radius R
(except the "V" here should really be an omega, which is
more commonly used for the "angular velocity" - and that's
what counts here). That acceleration can be used to
calculate the inward force on a mass M at the point,
courtesy of Newton's good ol' F = ma (or what would be
*perceived* as the "centrifugal force" felt by a mass being
whirled around a central point at this rate).
Bob M.
.
- References:
- Rain and the laws of physics
- From: Sean_Q_
- Re: Rain and the laws of physics
- From: Twibil
- Re: Rain and the laws of physics
- From: David T. Ashley
- Re: Rain and the laws of physics
- From: Twibil
- Rain and the laws of physics
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