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. Grimble

    Time scales in Inertial Frames of Reference

    Hello, I am trying to understand the relationships of the time scales that obtain within different Inertial Frame of Reference. Not when viewing one frame from another, I am quite happy with the Lorentz factor for that. No it is how the local time scale, that measured by a stationary, local...
  2. e2m2a

    Torque relative to an inertial frame

    I have a thought experiment I cannot resolve. Maybe someone smarter than I can resolve this. Suppose we have a long, thin rod, rotating in the counter-clockwise direction around a pivot axis which is at the end of the rod with an initial angular velocity equal to w. The axis is connected to a...
  3. e2m2a

    Orthogonal angle with respect to all inertial frames?

    Here is a thought experiment that I cannot resolve. Maybe someone smarter than I can do this. Suppose we have a long, thin rod rotating in the counter clockwise direction. The rod rotates around an axis which is connected to one end of the rod. The axis is attached to a second object which...
  4. R

    Inertial forces in crank slider mechanism

    I was little confused about taking inertial forces into significance while calculating piston effort in a piston crank slider arrangement. I read an analysis of various forces acting in a piston cylinder arrangement in a book yersterday, and while calculating piston effort(net force on piston...
  5. B

    Solving Non-Inertial Frame Homework: Spring Force, Mass, Acceleration

    1. Homework Statement A light spring force const. k hands from ceiling of an accelerating lift with a block of mass m attached to its bottom end. Block is held stationary (in lift frame) with the string at its equilibrium length while the lift is accelerating at a rate Ag where A is between...
  6. B

    Non-Inertial Frame Homework: Find Lift Acceleration

    Homework Statement A passenger holding a parcel mass m is standing in a lift which is being accelerated upwards by a constant force F. Total mass of life plus passenger is M. First q asks: what is the accel of the lift? Homework Equations The Attempt at a Solution So i know i...
  7. S

    Earth is a inertial frame of reference

    hi all of u WHAT IS INERTIA? and Earth is a inertial frame of reference or non inertial frame of reference? tell me briefly.
  8. L

    Calculate INERTIAL MASS of proton traveling close to speed of light

    Homework Statement A proton is traveling with a speed of v = 2.993x108 m/s. Calculate the value of the inertial mass for this proton. Assume that the speed of light is c = 3.000 x 108 m/s and that the mass of the proton is 1.673 x 10-27 kg. Note: Do your calculations to 4 significant...
  9. M

    STRACT: Inertial Frames in Special and General Relativity

    How are inertial frames defined in Special and General Relativity? In Newtonian physics, an inertial frame is usually defined as one in which N2 holds. Clearly this cannot be the same definition as for SR. In GR an inertial frame is one in which SR holds (I think). However, there is now a...
  10. G

    Inertial Frames: Is 'Absolute Rest' Possible?

    Hello... learning to post and into the appropriate forums. Also, can you delete previous post and how? Quick question: Since time as we know it does not or can not 'stop'... Is there such a thing as an intertial frame at 'absolute rest'? Thank you for any and all responses. Bye G
  11. G

    Equilibrium in Multiple Inertial Frames

    Two massive lead balls are sprayed with a thin veneer of positive charge. They are isolated and at rest in inertial frame K. The positive charge is such that the electrostatic force of repulsion exactly cancels the gravitational force of attraction. Viewed from frame K’, the Lorentz force on...
  12. B

    Changing the inertial reference frame to follow a mass in a collision

    Homework Statement We could change to inertial reference frame in a collision to follow a mass. But what would the down side be if we did? Homework Equations Vf1=(M1-M2)/(M1+M2)*Vi1 +2M2/(M1+M2)*Vi2 Vf2=2M1/(M1+M2)*Vi1 +(M1-M2)/(M1+M2)*Vi2 The Attempt at a Solution This question...
  13. K

    Time dilation and non inertial reference frames.

    Homework Statement A clock chimes every hour, on the hour in it's rest frame, is it possible for an observer to measure the time between chimes less than an hour? Homework Equations t = \gamma t0 The Attempt at a Solution I understand that if an observer traveling in the frame S'...
  14. T

    How Do You Calculate Normal Force on an Inclined Plane in a Moving System?

    Homework Statement |\ |--\/\ |----\/ |-----\ Given inclined plane with mass M. The angle of inclination is Alpha (from the horizontal plane). The plane has no friction. On the plane block with mass m. The whole system is moving rightwards with acceleration A0. Find the N normal...
  15. M

    Does c-invariance in SR postulate need inertial frames ?

    2 textbooks I have give postulate 2 of SR as: "The speed of light in vacuum is constant in all inertial reference frames". But "Classical Dynamics" by Jerry B. Marion has: "The velocity of light in free space is a universal constant independent of any relative motion of the source and...
  16. G

    Confusion about a laser shining perpendicular to a moving inertial frame

    I found this nice book on Google http://tinyurl.com/yh2y2zb that does a great job explaining relativity, however, even though the conclusions make perfect sense to me so far, I'm stuck on a conceptual issue when reading over the classic thought experiments that makes me feel like I'm still...
  17. R

    Acceleration in an inertial worldline?

    I think I'm beginning to understand general relativity. After doing some dabbling on the history of inertial frames vs accelerated frames from the time of Aristotle I've gotten to Einstein. Finally wrapped my mind around how an object in free fall is considered to be an inertial frame as...
  18. R

    Inertial Frame of Reference & Equilibrium

    Is it safe to say that any object in an inertial reference frame is at a state of equilibrium? If so.. is it safe to say the opposite: that any object in a state of equilibrium is in an inertial reference frame?
  19. G

    Calculating Time Dilation in Inertial Frames

    Homework Statement A rocket travels in a straight line with speed 0.6c, where c is the speed of light in a vacuum. A wrist-watch is on board the rocket. The rocket moves past a clock tower on the earth. a. In the inertial frame where the tower is at rest, how long does it take the watch (on...
  20. G

    What is the Centrifugal Force in Relation to Inertial Frames?

    I am confuse of what is inertial frame of reference. Can someone explain that to me? I need a clear explanation starting from the beginning to the end, and if possible, give me some set of example.
  21. N

    Gravitational mass vs inertial mass

    In Sean Carroll's lecture book is written: "... if gravitation did not couple to itself, a "gravitation atom" (two particles bounded by their mutual gravitational attraction) would have a different intertial mass (due to negative binding energy) than gravitational mass..." Would you please...
  22. T

    Inertial mass, gravitational mass, and the Higgs

    If we explain the origin of inertial mass with the Higgs mechanism, how do we explain the origin of gravitational mass? In other words, how does the Higgs mechanism contribute to the gravitational field of a particle? (Note: the closest thread I've found to this is...
  23. S

    Exploring the Differences between Inertial and Static Friction

    HI guys, i was wondering what is the difference between inertial and static friction? If a car is on a frictionless ground, does it have static friction and the inertial is the same even if it is on a rough surface right?
  24. M

    Understanding Inertial Frames: How to Determine if You're in One

    Is there really such a thing as an inertial frame? How would we know for sure if we were in one? Looking at space, things are moving and accelerating all over the place, it would seem impossible to tell whether a frame is really inertial or not. Imagine you are in space and everything around...
  25. A

    Is a falling elevator a valid inertial frame?

    Is a falling elevator a valid inertial frame? The title about says it. Is a body, (frame) free falling in a gravitational field a valid inertial frame as defined by SR? Thanks
  26. W

    Is the Pen on My Desk a Geodesic and Is My Room an Inertial Frame?

    Hi, I was wondering: I'm sitting at my desk and on my desk lies a pen. Does the pen describe a geodesic? And is the room I'm sitting in an inertial frame? I think the pen doesn't describe a geodesic because it's not in free fall and i think my room is a good approximation of an inertial...
  27. J

    Calculating Maximum Inertial and Connecting Rod Forces in a Piston Mechanism

    Ok so here's the question I am looking at. A piston and cylinder mechanism is connected to a crank shaft. The crank is 50mm long, the connecting rod 250 mm long and the piston has a mass of 150g. If the engine speed is w rad/sec and the crankshaft torque T Nm calculate:- i) Max inertial...
  28. R

    Dual of the inertial observer

    If an inertial "observer" or state has mass and no rotation, then a massless state with rotation (i.e. having maybe a generalized rotation such as "spin," e.g. a photon) seems to be dual to that state. Would this viewpoint then take the photon as a "matching" channel or "process" for...
  29. T

    What Drives the Mass of Particles According to Theoretical Physics?

    A favourite - good grief no. I don’t even understand some of the Higgsless models. I’m not a theoretical physicist. For one thing, my maths isn’t up to it. No, it’s more of an unease with the Standard Model, even though the Standard Model has good agreement between experiment and theory in the...
  30. N

    Local Inertial Frame: Understanding Riemann Curvature & Metric Tensor

    Dear PF could you advise me Whether I understand properly or not: In an arbitrary space-time (with an arbitrary curvature) in any sufficiently little region we can go to Local Inertial Frame of Reference - sit into the free falling lift. Being there our experiments are the same as we have...
  31. T

    Exploring Inertial Mass and Time Travel Possibilities

    No pitchforks please (and lay off the caps with the big 'D' on them too) Following staying up until 4am (all good stories start like this), and making small talk with a friend doing a degree in physics, we both decided to harp on about theoretical theories such as string etc, and as hours...
  32. R

    Newton's laws and non inertial frame of reference

    Hi all Why do we actually say that Newton's laws do not hold for non inertial frames. can you folks give me an example of how Newton's laws collapse in an non inertial frame(if they do at all)
  33. M

    Proving Particle Velocity Exceeds c in All Inertial Systems

    Homework Statement Show that if an hypothetical particle has v>c in a inertial system , v>c in any other inertial system Homework Equations The Attempt at a Solution
  34. E

    Is there inertial mass-gravity equivalece principle with photons?

    The equivalence principle in GR states inertial mass and gravity are equivalent, what about massless particles?
  35. C

    Special relativity inertial reference frames.

    [b]1. Suppose the space time co-ordinates of two events in inertial frame S are as follows: Event 1: x1=x0, t1=x0/c y1=z1=0 Event 2: x2=2x0, t2= x0/2c y2=z2=0 Show that there exists an inertial frame s' in which these events occur at the same time (i.e t1'=t2') and find the value of time...
  36. T

    How do you tell you are not in inertial frame of reference

    While explaining about inertial and non-inertial frame of reference, people give this example-- http://www.phys.unsw.edu.au/einsteinlight/jw/module1_Inertial.htm if you don't wish to follow the link, here is a simple explanation---> there are two person and a rotating disk. Person A is in...
  37. W

    SR Inertial Frame Scenario Confusion

    I'm new to the study of SR and GR. I have a question that I have not been able to find any discussion about. In the case of two frames of reference where we are comparing events from the point of view between a 'stationary frame' (inertial) to an excelerating frame like the twin paradox is...
  38. C

    Spacetime we are able to distinguish between different inertial frames

    A professor told me that in our spacetime we are able to distinguish between different inertial frames because the cosmic microwave background looks different. If this is true then what spacetime do we live in? What would it look like mathematically. Would the det(g) not be negative?
  39. G

    Equivalence of inertial & gravitational mass-I need a sanity check.

    Equivalence of inertial & gravitational mass--I need a sanity check. Einstein, in his 1916 book Relativity, illustrates the equivalence of gravitational and inertial mass using the example of a braking train. The example begins with the train at rest (of course) and the scenery moving to the...
  40. G

    Inertial Propulsion Discussion: Energy Conservation

    In the follow link we are having a discussion about inertial propulsion: http://www.gyroscopes.org/forum/questions.asp?id=994 Bellow I transcript an open question that I’d like to share with you: The question is: How will be the energy conservation in the following experiment: “These...
  41. T

    Rotating Earth as an inertial frame

    According to the principle of relativity - a postulate for Einstein's SR and GR - any frame of reference is as valid as any other for describing phenomena and the laws of physics will be the same in the chosen frame of reference as in any other frame of reference. Taking the rotating Earth as a...
  42. C

    Inertial Charges: Magnetic Forces Relative?

    I was wondering whether or not a charge must be accelerating to produce a magnetic field. If the charge is moving at a constant speed does it create a magnetic field? I f I took a van de graff generator onto an airplane moving at a constant rate, could I measure a magnetic force? Or are magnetic...
  43. N

    Gravitational vs Inertial Mass

    (I realized I have a confusing post title but can't figure how to edit it..It should read "Gravitational curvature vs gravitational force" Under 'mass' Wikipedia makes a statement:
  44. C

    Newton's Second Law and Inertial Frames Of Refence

    I have a question about Newton's Second Law and Inertial Frames of Refrence. It is canon that Newton's Second Law is only applicable in an inertial frame of refrence. Newton's Second Law is the net force acting on a body is equal to the time rate of change of the body's linear momentum...
  45. R

    Inertial Frame of Reference: Is it an Ideal Concept?

    It is sometimes heard that inertial frame of reference does not actually exists and is only an ideal concept. What do you guys think? Say, for example, An object is placed far away from all objects that can exert force on it. A reference frame is taken by taking the origin and axes fix in...
  46. C

    From an inertial refernce point, how to tell if a particle is free?

    Homework Statement From an inertial reference frame S, the vector position of a particle of mass m1 = 1kg is given by r1(t)=(tx-hat - t^2y-hat)m. The vector position of a particle m2=2m1 is given by r2=(t)=(tx-hat +t^3y-hat)m Is particle #1 free along the y-direction? Explain...
  47. U

    Is a reference frame fixed to a photon an Inertial Frame?

    Hi All, I am a bit confused about reference frames and inertial frames. According to the first postulate of special relativity (if I'm right), all physical laws take their simplest form in an inertial frame, and there exist multiple inertial frames interrelated by uniform translation...
  48. V

    Inertial frames vs velocity vectors

    Hi all. I was trying to imagine gravitation as a causal effect of time dilation and have relatively little schooling so... With frames of reference obviously a high degree of time dilation is attained with a relative velocity close to c. however I understand a large stellar object such as a...
  49. A

    What is an inertial frame of reference?

    Homework Statement What is an inertial frame of reference? Homework Equations -A particle at rest or moving at a constant velocity in an inertial frame of reference implies that the sum of the forces acting on the particle is zero -The tendency of a body to keep moving once it is set in...
  50. C

    Definition of inertial frame

    since last time i post about the defiinition, i read up about it, how i am still a bit unclear after reading few more post about this topic : einstein: a set of frames which move without acceleration to one another and that the laws of physics hold in the simplest-is the a definition or that...
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