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alvaros
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what is an inertial frame of reference ?
Simple ?
Simple ?
alvaros said:what is an inertial frame of reference ?
Simple ?
I don't understand. Note that this thread is post in the Classical Physics section. I suppose that, at the end, someone will refer to relativity. But, if you like, and its possible, let's talk as we are at 1900.it's the immediate space-time co-oridinate in which the observer is not in motion.
rotation respect to what ?with constant velocity along a straight line and without rotation.
What are fictitious forces ?fictitious forces
alvaros said:meopemuk:
rotation respect to what ?
Again: rotate respect to what ?The reference frame should not spin (rotate) around its own axis
Are you shure that distant stars ( the universe ) are not rotating ? Why ?distant stars should not be seen in a circular motion
Actually,... it is such a fundamental notion in physics, than it cannot be reduced to anything simpler. However, I don't think there is any controversy. We will all agree whether the frame is inertial or not when we see it.
alvaros said:Are you shure that distant stars ( the universe ) are not rotating ? Why ?
alvaros said:What are fictitious forces ?
An inertial frame of reference, or inertial reference frame, is one in which Newton's first and second laws of motion are valid. In other words, a reference frame that is neither rotating nor accelerated.
Hence, with respect to an inertial frame, an object or body accelerates only when a physical force is applied, and (following Newton's first law of motion), in the absence of a net force, a body at rest will remain at rest and a body in motion will continue to move uniformly—i.e. in a straight line and at constant speed.
A fictitious force, also called a pseudo force or d'Alembert force, is an apparent force that acts on all masses in a non-inertial frame of reference such as a rotating reference frame. The force F does not arise from any physical interaction, but rather from the acceleration a of the non-inertial reference frame itself. Due to Newton's second law F = ma, fictitious forces are always proportional to the mass m being acted upon.
You keep saying that- as if it meant something! Even in classical mechanics, velocity or speed is alway relative to something. Rotation, however, is acceleration and so is not relative.Alvaros said:Again: rotate respect to what ?
alvaros said:rotation respect to what ?
HallsofIvy said:You keep saying that- as if it meant something! Even in classical mechanics, velocity or speed is alway relative to something. Rotation, however, is acceleration and so is not relative.
This force means nothing and is not related to the mass(1). Tell about a real example of what you are saying.Dividing the observed acceleration by the mass(1) yields something with units of force.
The tension of the rope that holds the rotating mass.But what exerts the "centrifugal force,"
I agree. So there are absolute not rotating axes that are the same in all the universe and all inertial reference frames must not rotate respect to these axes. And thes axes don't need to refer to distant stars, but you need something material ( with mass ) to discover them. Do you agree ?Rotation, ( ... ) is not relative.
Id like to hear something about that. Dont you understand what I am saying in my poor english? Did you know the paradox ? Did you read anything on any book related/explaining this paradox ?Do you know the paradox ( Newton ) of a bucket whith water. If the bucket rotates nothing happens but if the water rotates the surface of the water is like a "V". Newton said: the next book I will explain that... He never explained it.
jtbell said:To me, in the classical physics context, fictitious forces are "forces" that have no agent. That is, there is no object that is their ultimate "source." Gravity is not a contact force, but one can nevertheless say e.g. that gravitational force that makes an object fall, is exerted by the Earth, although indirectly. Likewise for electric and magnetic forces, although with these we also have to include time delays for propagation of electromagnetic waves etc.
But what exerts the "centrifugal force," "Coriolis force," and "transverse force" on an object in a rotating reference frame?
alvaros said:The tension of the rope that holds the rotating mass.jtbell said:But what exerts the "centrifugal force,"
alvaros said:Too many ideas to discuss but..
D.H:
D H said:Dividing the observed acceleration by the mass yields something with units of force.
This force means nothing and is not related to the mass(1). Tell about a real example of what you are saying.
HallsofIvy:
I agree. So there are absolute not rotating axes that are the same in all the universe and all inertial reference frames must not rotate respect to these axes. And thes axes don't need to refer to distant stars, but you need something material ( with mass ) to discover them. Do you agree ?
If there is no agent there is no reaction ( Newton 3rd law ). I wouldn't call them "forces"To me, in the classical physics context, fictitious forces are "forces" that have no agent.
Centripetal and centrifugal are action/reaction. Do you agree? If you dont, which are the reaction forces of centripetal/centrifugal ?That's the centripetal ("towards the center") force that causes the object to accelerate continuously towards the center of its circular path, in an inertial reference frame. It's very real.
I'm talking about the centrifugal ("away from the center") force that apparently pulls the object outwards, in a (non-inertial) rotating reference frame. The rope can't pull or push outwards on the object.
Sorry, I just copy and paste...That should have been "multiplying", not "dividing".
If I undestand, the rotation of distant stars has been measured. Respecto to what ?We use the distant stars as to define our best estimate of what constitutes an inertial frame. We do this because the measurements are so incredibly precise. The International Celestial Reference Frame differs from J2000 by an incredibly small rotation rate, which differs from Mean-of-1950 by a slightly larger (by still very small) rotation rate.
alvaros said:If there is no agent there is no reaction ( Newton 3rd law ). I wouldn't call them "forces"
No. Example: You are on a merry-go-round. You observe someone standing still on the ground outside the merry-go-round. You see that person as accelerating. There is no real centripetal force (the person is standing still). The apparent acceleration results solely because you are observing the person from the vantage point of a rotating frame.Centripetal and centrifugal are action/reaction. Do you agree?
If I undestand, the rotation of distant stars has been measured. Respecto to what ?
But I like to get answers about these statements (if you are so kind in answering me):
1- There are absolute not rotating axes
2- All inertial reference frames must not rotate respect to these axes
3- you need something material ( with mass ) to discover them
alvaros said:Centripetal and centrifugal are action/reaction. Do you agree?
alvaros said:what is an inertial frame of reference ?
Simple ?