thomas malloy wrote:
Harry Veeder wrote:
Michel Jullian wrote:
Doing calculations in an accelerating frame makes me sick I am afraid
;-) But I guess it would be the same force, since it's not a
ficticious one like e.g.
the centrifugal force.
Hum; ficticious force? Isn't the force that causes water going down
drain to spin the centrifugal force?, what about tornados?
Sigh... A "fictitious" force is not a "fictional" or "nonexistent" or
"false" or "non-real" force.
"fictitious" is a technical term, just like the phrase "imaginary"
number, or even the word "force". It is typically better to call such
forces "inertial" rather than "fictitious" because it avoids pointless
arguments over whether or not "fictitious" forces are "real".
A "fictitious" (or "inertial") force is one which appears in an
accelerated reference frame, and can be made to vanish (from the
analysis) by performing the analysis in an inertial frame. Such forces
are also marked by the fact that they affect _all_ objects equally,
independent of mass, charge, or other properties; this is quite
different from the way other forces, such as electromagnetic forces,
act. Non-inertial forces are generally somewhat selective as to which
objects they act on.
For example, a careful analysis of the motion of a rotating object, done
in an inertial frame, using Newtonian mechanics, has no need of the use
of "centrifugal" or "Coriolis" forces. Those forces appear in the
analysis only when doing the analysis in a rotating frame. As such,
they are called "inertial" forces, or more commonly "fictitious" forces.
When you are actually _in_ a rotating frame, such as a car going around
a corner, you naturally "think" about the situation from the POV of that
frame, and in that frame, the centrifugal force -- and the Coriolis
force -- are both quite real, even though they are /called/ "fictitious"
forces.
Here's a little demonstration of the Coriolis force: Next time you're
in the car, turn on the heater or AC and arrange the air stream so it
goes just past your head on one side or the other. Now, when the car
turns left, note what happens; when the car turns right, note what
happens. Chances are, when the car turns in one of those directions,
you'll briefly find the stream of air blowing directly into your face
rather than just past your head. The Coriolis force causes the moving
stream of air to bend while the car is rotating.
The emdrive also comes to mind. If it works, is that a frame based
phenomena?
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