Register to reply 
How inertial frame of reference differs from noninertial frame..? 
Share this thread: 
#1
Apr2012, 06:00 AM

P: 114

We know that we can't say whether we are at rest or uniformly moving if we're in a einstein cage..but if the same medium is accelerating/decelerating can we being inside(and can't see outside) claim abt state of cage..?I ve read that a noninertial can be converted to inertial by incorporating a fictious force..?? Does this fictious force has any orgin.If yes,where this origin disappears when cage stops accelerating.?If there are 2 bodies inside a cage which is accelerating uniformly,does 1 body see other body in rest..?



#2
Apr2012, 06:29 AM

Mentor
P: 17,509

You can tell if your cage is inertial or not simply by using an accelerometer comoving with the cage. If it reads 0 then the cage is inertial.



#3
Apr2012, 06:46 AM

P: 114

well..I remember a example stating why noninertial frames can be recognised being inside.When the person inside a cage tosses a coin,if the coin falls back in this hand then he's in inertial frame else if it falls right ahead of him or behind he's in decelerating or accelerating frame..but why does this phenomenon occur,why can't the coin in same way as inertial frame fall back into his hand by consuming the acceleration in the air also while tossed



#4
Apr2012, 06:59 AM

Mentor
P: 17,509

How inertial frame of reference differs from noninertial frame..?
If the cage is inertial then the coin won't fall back into his hand, it will continue to move in a straight line at a constant speed. That is Newtons first law.



#5
Apr2012, 07:05 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,682

That is assuming no external forces. Am I in an "inertial coordinate system" sitting here in front of my computer? If I were to toss a coin in the air, it would come back to my hand!



#6
Apr2012, 07:45 AM

P: 114

Any body inside a inertial frame is a source of noninertiality because the body is held intact by forces..does that mean there's NO INERTIAL FRAME in known physical applications.?



#7
Apr2012, 08:52 AM

P: 4,194




#8
Apr2012, 09:50 AM

Mentor
P: 17,509




#9
Apr2012, 01:16 PM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,682

Ah. So a room stationary on the surface of the earth is "noninertial" and a room falling with nonzero accleration due to gravity is "inertial".



#10
Apr2012, 02:03 PM

Sci Advisor
PF Gold
P: 1,848




#11
Apr2012, 02:03 PM

P: 4,194

Inertial frames are those where all inertial forces disappear (all Newtons Laws hold). The difference is only the classification of gravity as a interaction or inertial force respectively. 


#12
Apr2012, 03:59 PM

Sci Advisor
P: 2,944

The coin trick has to assume that the coin is not charged, or that there is no external electromagnetic field (or both). Only gravity gets to modify what you call "inertial" or not.



#13
Apr2712, 10:49 PM

P: 114

My question is still not answered completely.! Whats use of fictious force in this context..and how to convert a noninertial frame to inertial frame.and does a body appear stationary when watched by a object in its accelerating frame.



#14
Apr2712, 11:14 PM

P: 3,967

Now if we have object accelerating with constant proper acceleration then there exists a non inertial reference frame, in which the object will appear stationary. If we have an inertial object that is accelerating from the point of view of a non inertial reference frame, then there is also exists an inertial reference frame in which the object appears to be stationary. This is trivially obvious. However, if we have a non inertial object experiencing proper acceleration, then there is no inertial reference frame where the object appears stationary for more than an instant. Conversely, if we have a inertial object with coordinate acceleration as measured in a non inertial reference frame, then there is no non inertial reference frame where the object appears stationary for more than an instant. 


#15
Apr2812, 10:50 AM

Sci Advisor
PF Gold
P: 1,848

The concept of "fictitious force" arises in Newtonian (nonrelativistic) physics. For example, relative to a rotating frame of reference, Newton's 2nd law F=ma=dp/dt doesn't work, but we can make it work by adding in a centrifugal "force" and a coriolis "force". Because these forces don't exist in an inertial frame, these forces are usually described as "fictitious forces".
In relativity this is taken account of by the difference between a coordinate derivative and a covariant derivative. Newton's law in a noninertial frame becomes[tex] F^\alpha = \frac{\mbox{D} P^\alpha}{\mbox{D} \tau} = \frac{\mbox{d} P^\alpha}{\mbox{d} \tau} + \Gamma^\alpha_{\beta\gamma} U^\beta P^\gamma [/tex]The term involving [itex]\Gamma^\alpha_{\beta\gamma}[/itex] is the "fictitious force" term and becomes zero in an inertial frame. In general relativity, gravity becomes a fictitious force. A freefalling inertial observer feels no force of gravity. An observer on the Earth's surface is experiencing a proper acceleration upwards and zero acceleration relative to the Earth. The fictitious weight of the observer makes Newton's Law work relative to the Earth's surface. 


Register to reply 
Related Discussions  
Inertial and noninertial frame of reference  Introductory Physics Homework  3  
Major difference of Inertial and noninertial frame of reference ?  Special & General Relativity  3  
Inertial frame of Reference?  General Physics  14  
Is a reference frame fixed to a photon an Inertial Frame?  Special & General Relativity  3  
Inertial reference frame  General Physics  4 