# New definition of a non inertial frame of reference.

#### avito009

The present definitions of non inertial frame of reference are vague. Some would define it to mean that a non inertial reference frame is one which does not obey newtons first law. But we can define a non inertial frame of reference in this way.

"A non inertial reference frame would be one which obeys only the second law of newton F=ma."

It cant obey the first law since first law applies only in an inertial frame of reference and the third law cant apply precisely due to the reason mentioned in my earlier thread by observing the bus moving forward and you pushed backward and pressed towards your seat.

#### topsquark

Forum Staff
The present definitions of non inertial frame of reference are vague. Some would define it to mean that a non inertial reference frame is one which does not obey newtons first law. But we can define a non inertial frame of reference in this way.

"A non inertial reference frame would be one which obeys only the second law of newton F=ma."

It cant obey the first law since first law applies only in an inertial frame of reference and the third law cant apply precisely due to the reason mentioned in my earlier thread by observing the bus moving forward and you pushed backward and pressed towards your seat.
An inertial frame is one where the frame moves at constant speed with respect to another inertial reference frame. The problem is finding an inertial frame to begin with. Even Newton had trouble with that one. But supposing we can find at least one approximate inertial reference frame (the surface of the Earth will do for most purposes), then a non-inertial frame is simply one that is not inertial. A non-inertial reference frame is typically defined by saying the frame is traveling with an acceleration as measured by an inertial frame.

-Dan

#### Pmb

PHF Hall of Fame
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The present definitions of non inertial frame of reference are vague. Some would define it to mean that a non inertial reference frame is one which does not obey newtons first law. But we can define a non inertial frame of reference in this way. Let me Edwin why. Essentially what you're proposing is identical to "an inertial frame is one I which Newton's first law holds true." Since a non-inertial frame is one which is not inertial this means that a frame in which Newton's first law does not hold true is

"A non inertial reference frame would be one which obeys only the second law of newton F=ma."
Why change the definition? It's hardly a vauge one as you claim, especially since nobody has conceived of a situation where it fails to work. Yours implies that a non-iniertial frame doesn't obey Newton's third law when it actually does. I can't see the benefit of your definition. Should it mean that o other law of physics applies too?

It really doesn't contain much more than the current definition anyway since its logically identical to how an inertial frame is defined.

Sorry. Better luck next time.

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