# The validity of classical physics (split from: DWFTTW)

1. May 22, 2010

### ajaybali

The purpose of this post is to present the established tenets of classical physics and to create a point where this thread can be split if there is still disagreement as to the validity of these tenets.

If the participants in this thread agree to the split, all further discussion of the validity of alternate inertial reference frames, the special nature of an earth based reference, the treatment of Kinetic energy being an absolute property of an object and not relative to the frame of reference and any other claims that invalidate classical physics shall be split to the new thread.

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Title: The validity of classical physics [split from Down Wind Faster Than The Wind]

In Newton's laws of motion, there is no factor of an absolute reference for position or velocity.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion
Quote:
First law
It is possible to select a set of reference frames, called inertial reference frames, observed from which a particle moves without any change in velocity if no net force acts on it. This law is often simplified into the sentence "A body continues to maintain its state of rest or of uniform motion unless acted upon by an external unbalanced force." This law is known as the law of inertia.
Second law
Observed from an inertial reference frame, the net force on a particle is proportional to the time rate of change of its linearmomentum: F = d (mv) / dt. Momentum mv is the product of mass and velocity. Force and momentum are vectorquantities and the resultant force is found from all the forces present by vector addition. This law is often stated as "F = ma: the net force on an object is equal to the mass of the object multiplied by its acceleration."
Third law
Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence "To every action there is an equal and opposite reaction."
This means that we can investigate the behavior of physical systems in an equivalent inertial frame that is chosen to be more convenient. For instance, the physics of a vehicle traveling down a straight level road with a tail wind can be investigated by placing that vehicle on a similar surface that is moving at a constant velocity relative to the observer so that the same effective tail wind will not be moving relative to the observer and the vehicle when traveling at the speed of the tail wind will also not be moving relative to the observer.

This split thread has been created to discuss the validity of using alternate inertial reference frames to examine or model classical physical interactions [between the limits where relativity and quantum effects are significant] and related topics such as motion relative to the ground being somehow special and kinetic energy having a specific value independent from the frame of reference. I don't understand the contrary view so I'll let the other posters present their side.

Last edited by a moderator: May 23, 2010