What is Inertial: Definition and 496 Discussions

In classical physics and special relativity, an inertial frame of reference is a frame of reference that is not undergoing acceleration. In an inertial frame of reference, a physical object with zero net force acting on it moves with a constant velocity (which might be zero)—or, equivalently, it is a frame of reference in which Newton's first law of motion holds. An inertial frame of reference can be defined in analytical terms as a frame of reference that describes time and space homogeneously, isotropically, and in a time-independent manner. Conceptually, the physics of a system in an inertial frame have no causes external to the system. An inertial frame of reference may also be called an inertial reference frame, inertial frame, Galilean reference frame, or inertial space.All inertial frames are in a state of constant, rectilinear motion with respect to one another; an accelerometer moving with any of them would detect zero acceleration. Measurements in one inertial frame can be converted to measurements in another by a simple transformation (the Galilean transformation in Newtonian physics and the Lorentz transformation in special relativity). In general relativity, in any region small enough for the curvature of spacetime and tidal forces to be negligible, one can find a set of inertial frames that approximately describe that region.In a non-inertial reference frame in classical physics and special relativity, the physics of a system vary depending on the acceleration of that frame with respect to an inertial frame, and the usual physical forces must be supplemented by fictitious forces. In contrast, systems in general relativity don't have external causes, because of the principle of geodesic motion. In classical physics, for example, a ball dropped towards the ground does not go exactly straight down because the Earth is rotating, which means the frame of reference of an observer on Earth is not inertial. The physics must account for the Coriolis effect—in this case thought of as a force—to predict the horizontal motion. Another example of such a fictitious force associated with rotating reference frames is the centrifugal effect, or centrifugal force.

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  1. O

    Speed of light in non inertial frames

    sorry to bring this up again, i have just started special relativity and the constancy of c is a bit confusing, i get how c is the same in all inertial frames but what about accelerating frames? do observers in acceleration still see c as a constant? i have seen many forum posts and they always...
  2. A

    Quick question about inertial frames of reference

    Homework Statement If you are on the merry-go-round going in a circle at constant speed, are you looking at the world in an inertial, or non-inertial frame of reference? How do we tell whether from one's viewpoint, they are looking at something from an interial or non-inertial frame of reference?
  3. M

    Inertial frame dependent on mass?

    My question is: Is the inertial reference frame dependent on mass? In re-reading materials on the topic of special relativity, I have noticed something that passed my attention previously. Within the inertial reference frame, the mass of test particles isn't necessarily dependent on how they...
  4. L

    Non inertial frame: Speed of light

    The speed of light is not constant in a non-inertial frame; the light accelerates with the acceleration of the observer in reverse direction. Consider the following problem: If a light pulse is created in an inertial frame at some time, t<0 (say t=-10); the light pulse moves at velocity c...
  5. G

    Physical definition of inertial reference frames

    Dear all, I'm trying to understand better why gravity makes impossible to physically define an inertial reference frame. Firstly, we must have an operational procedure that allows us to physically define an inertial reference frame. Secondly, we must show that gravity makes this procedure fail...
  6. R

    Inertial vs accelerating frame

    I'm free-falling towards a planet. Inertial or not? I suppose this is a postulate of general relativity isn't it? When I'm studying special relativity I would say Non-inertial, but then if I think about how I cannot really tell if I am accelerating or just traveling a constant...
  7. Z

    Exploring Inertial Reference Frames in the Expanding Universe

    Are galaxies, quazars inertial reference frame? I think they are at rest or moving at constant velocity relative to the expanding space. But what is the coordinate system to the scale of the whole universe that can describe these inertial reference frames appropriately? Is the coordinate...
  8. D

    What Determines the Speed of a Spacecraft in Special Relativity?

    Homework Statement Usually in physics problem on special relativity, the state that this particular spaceship is traveling at, say, 0.6c. Question is, where does this 0.6c come from? If the speedometer in the cockpit reads 0.6c, does it mean that the observer will look and think that it...
  9. M

    Q: Inertial Frames & Detecting Motion

    In a true inertial frame inside a train compartment, it is impossible to do an experiment that can tell you if you are moving or not. This is a key consequence of Newton's Laws Of Motion. However, if someone had a neutrino detector, or a Higgs detector (assuming they exist), wouldn't it be...
  10. M

    What's an inertial frame of reference?

    The Earth is an approximately inertial reference frame since it's acceleration with respect to the stars is very small. But if a group of stars is accelerating with respect to another group of stars which group is the inertial frame? Or thinking on an even larger scale, if a universe is...
  11. H

    How Do The Definition Of Inertial In Relativity Relate To General Mechanics

    Hi all, I am struggling with the following problem, and so far I have not found a satisfying solution. The problem is that the definitions of "Inertial" and "Non-Inertial" in relativity appear to me as being at opposites with the ones in Classical Physics (and of course I am probably missing...
  12. S

    Is the magnitude of the Lorentz force always the same in different inertial frames?

    Sorry if I should be posting as homework, but it's not homework anymore and I'm just curious about the answer. My question is simple and doesn't require answering the actual homework question I had. If there is a force on a charge in one inertial frame of reference, will there also be a force...
  13. S

    Calculating Light Travel Time in a Moving Reference Frame

    If I am standing at the bottom a spaceship of a Length L moving at a certain speed v (let's say half light speed so that relativistic effects aren't negligible), how would I go about calculating how long it would take the light beam to reach the top of the spaceship? In Newtonian mechanics...
  14. C

    Inertial Navigation Integration FIlter

    Hello, I am trying to create a filter that can integrate inertial measurements with GPS measurements. My inertial sensors are a yaw axis gyro, an odometer, and possibly a 3axis accelerometer. Could you please help me with some guidance? I have read papers, articles and books on the subject but...
  15. M

    How to be an Inertial Observer?

    I think this "elephant-in-the-room" issue is important enough to deserve its own thread. I believe it is at the root of many of the disagreements that repeatedly occur on this forum. So I copied my last posting over from the "The case for True Length = Rest Length" thread. Here is that...
  16. S

    Inertial and non-inertial frame of reference

    Okay, so I know what inertial and non-inertial frames of reference are: 1. Inertial is when Newton's laws of motion hold. 2. Noninertial is when they do not hold (the object is accelerating without a force). And I have a few examples as well, such as when you are is in a car and the car is...
  17. S

    Synchronizing Atomic Clocks in Inertial Motion: Planet or Black Hole?

    Say there are two atomic clocks floating through space, both completely stationary with respect to each other. They are exactly synchronized, and not under the influence of any significant gravitating bodies. One is significantly farther ahead in the direction of motion than the other, but they...
  18. Y

    Let a clock A be at rest in an inertial frame and let a clock B rotate

    Let a clock A be at rest in an inertial frame and let a clock B rotate around it with constant velocity and constant distance from A. Let v be the velocity of B relative to the inertial frame. Both clocks count how long it takes for B to rotate once. According to clock A, the time it takes is...
  19. G

    Inertial tensors & Center of mass?

    inertial tensors & Center of mass?? Hi, I am trying my best to program a simple flight simulator (or just movement for now!) and having problems. But whilst doing more research into it, I've come across a few things I am not doing, and can't really find a undersstandble answer too? I need...
  20. S

    Minimum energy and power, break-even; inertial fusion

    Homework Statement A small 50:50 D-T pellet of density p=3g/cm^3 is used for inertial fusion. Estimate minimum energy and power of the laser device required to heat the pellet to T=10^4 eV and to achieve the energy break-even condition Homework Equations Lawson criteria: nt>10^20...
  21. M

    Inertial Propulsion: The Potential of Eliminating Electron Mass in Graphene

    Electron Mass Effectively Eliminated in Graphene http://archive.sciencewatch.com/jan-feb2007/sw_jan-feb2007_page6.htm Since reading this I've been bothered by the niggling implications of a system in which the value of mass can be varied.. particularly with regards to propulsion. It...
  22. V

    Will the frame be inertial if no forces act on it?

    Hello :) An object is placed far away from all the bodies that can exert force on it. A frame of reference is constructed by taking the origin and axes fixed in this object. Will the frame be necessarily inertial? Hmm According to me, it should be an Inertial frame as No force acting on it...
  23. M

    Is a point (x distance from earth) inertial frame ?

    me and my friend were arguing (like always) about inertial frame ? to sum up i m just asking a straightforward question ? let say (for simplicity) there is just Earth and an other object in whole universe. a point whose distance from Earth is x. and dx/dt = 0. now is that point (which...
  24. J

    Inerital vs Non inertial reference frames: quick conceptual question

    Homework Statement I'm doing a problem in which an ant crawls in a circle on a spinning pottery wheel. Say I'm looking at the friction which holds the ant in place. It keeps the ant from slipping. Looking at it in the inertial frame of reference, I know that the centripetal force points...
  25. R

    A sliding puck analyzed from an inertial reference frame

    Homework Statement Located here:http://imgur.com/qP9fd.png" The Attempt at a Solution I don't know how to do this problem. First of all how do I approach it? Should I do a free-body diagram? Should it be done at position 1? How do I account for the different frame of reference...
  26. J

    Major difference of Inertial and non-inertial frame of reference ?

    Major difference of Inertial and non-inertial frame of reference ?? What is the major difference or differences of Inertial and non-Inertial frame of reference?? Is it only: Inertial - Constant velocity, obeys the law of inertia Non-inertial - Acceleration, disobeys the law of inertia
  27. 1

    Why do we treat earth and why does it work as an inertial frame

    Earth is clearly not an inertial frame, its in orbit and not following a single direction of movement. Why then do we treat it as one? Are there any slight differences in the laws of motion in a true inertial frame in contrast with those on earth?
  28. M

    Inertial navigation system

    I got a problem in which I need to simulate the position of an object given accelerations in two dimension and rotation in the third. Integrating the acceleration values twice would give me the position in the particular dimensions, and using the angular rotation I could get the position of the...
  29. B

    Problem in inertial reference frame

    Well, in principle, this problem seems very easy but I don't know the exact explanation.Here we go. We have a truck and a pack in its back.The bed of the truck is frictionless and the pack is stopped by a small piece of wood of something like that. The size of the pack is whatever(for...
  30. L

    Simple question about inertial frames of reference

    Hello, I know that this is going to sound stupid, so please forgive me, but could someone give me a brief and simple definition of what an inertial frame of reference is and what a non-inertial frame of reference is? Thanks, Louis
  31. P

    Block sliding down accelerated inclined (need inertial frame approach)

    Homework Statement A block of mass "m" is placed on an incline of angle \theta and mass "M", which is placed on a horizontal surface (the ground) and release from rest. Both the block and incline start accelerate. All surfaces are frictionless. Find the acceleration of the block with respect...
  32. M

    How to determine nature of frame (inertial/non inertial)?

    what is inertial frame of reference. lets say motion is in 2d universe (x,t) consider three points f,a and b the distance of a and from f be x and y respectively. for what equation (s) of motion f would be inertial frame of reference for a ? what does it mean that Newton's law hold...
  33. M

    Inertial navigation system using kalman filter

    Hello, Im working on estimation of inertial navigation system using kalman filtering. Can anyone help me finding the state space model of inertial navigation system used to estimate the states via kalman filter. An early response is needed.Thanks in advance.
  34. A

    Real Inertial Motion: A Discussion of Frame Independence

    REAL inertial motion? The question of the reality of motion and the Lorentz effects came up again in a recent thread where it was correctly pointed out that these subjects often devolve to arguments of semantics and subjective interpretations. It was also suggested that frame independence...
  35. Y

    Two travelers both in Inertial Frames

    The twin thing has been beat to a pulp on these forums - so maybe this got resolved somewhere along the way - if so - someone can point me to the solution. Otherwise here is the set-up. Assume two satellites are placed in orbit around a black hole, one is in circular orbit, the other highly...
  36. F

    How does an inertial force affect water movement in an open channel?

    I am working on a project where I have to calculate the affected water movement in an open channel. What I mean by affected water movement is the gallonage moved by an inertial force such as a stream of water discharged under pressure. For example: A 1" pipe is discharging 10 GPM into an...
  37. A

    Galilean Relativity & Inertial Frames

    I just want to make sure I understand this correctly. Please critique: Under Galilean relativity, Newton's Law of Inertia retains the same form under any inertial frame of reference. There are relative velocities between inertial frames but its possible to determine absolute velocities under...
  38. R

    Coriolis Acceleration and Inertial Frame

    Hi In my textbook they were doing a derivation of the acceleration of a projectile flying on Earth. Although they used the center of the Earth as the frame of reference, they ended up with the linear combination of 3 quantities for the acceleration of the projectile, one of which they said...
  39. M

    The scope of inertial time dilation?

    I am trying to resolve a number of questions concerning the scope of time dilation within the confines of special relativity, i.e. flat spacetime. For example, if I simply state that 2 inertial frames of reference pass each other with a relative and constant velocity [v], it is my understanding...
  40. E

    Inertial reference frames problem

    Homework Statement An example of an inertial reference frame is: A. any reference frame that is not accelerating B. a frame attached to a particle on which there are no forces C. any reference frame that is at rest D. a reference frame attached to the center of the universe E. a reference...
  41. B

    Newtons first law and inertial reference systems. (noob)

    Hi everyone, Recently i started a self-study in classical physics by reading through some books. In the section that described Newton's first law I stumbled upon something that did not make much sense. The following section of text got me confused. "If the net force acting on a body is...
  42. P

    GR: Local Inertial Frame & Poincare Invariance

    Is it possible to deifine local inertial frame which is Poincare invariant (in general relativity) (every manifold is locally flat, so we can chose coordinates which are almost pseudoeuclidean, but in what sense they might be Poincare invariant) Thanks.
  43. D

    Is Gravity an Inertial Force According to the Equivalence Principle?

    I've often thought that one way to restate the equivalence principle is that the force of gravity is a manifestation of using a frame that is not in free-fall. In other words, it's an inertial force akin to the Coriolis and centrifugal forces in a rotating frame of reference. However, I just...
  44. C

    Simultaneity of Events in Different Inertial Frames

    if two events are simultaneous in an inertial frame, then they would not be simultaneous in another inertial frame as long as they are separated in space.Equally the vice versa is valid.Does this not imply that it would be possible for one to see someone to be born and to be dead at the same time?
  45. N

    Gravitational and Inertial Masss

    Homework Statement Determine the relationship between inertial mass and gravitational mass. Homework Equations F=Ma The Attempt at a Solution To establish a relationship between gravitational and inertial mass they firstly need to be defined. Gravitational mass is the property...
  46. A

    Inertial navigation system books?

    Inertial navigation system books?? Hi, Kindly refer me a good book for the basic concepts of inertial navigation system or even any good website link.
  47. A

    Inertial reference frame for 2&3 law

    Does the concept of Inertial reference frame also applicable for 2nd & 3rd law of motion?
  48. A

    Understanding Inertial Properties: The Role of Mass in Resisting Motion

    Does only 'mass' as a prop. of an object responsible for resistance to change in motion?
  49. A

    Is symetry across inertial frames purely theoretical?

    Hi. If the twin paradox, etc, is not really a paradox because one twin experiences acceleration, then is the idea of recipricol time dilation etc due to symetry across inertial frames purely theoretical? What I mean is that could we ever find two inertial frames moving relatively to each other...
  50. P

    Light speed in a non Inertial frame of reference

    Does the principle of invariant light speed still hold in a non Inertial frame of reference? Thank you!
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