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. Like Tony Stark

    Measuring position and velocity from a non inertial reference frame

    I) For ##A##, the positition is ##\vec r=(0;V_0 . t;0)##. For ##B##, we have ##\vec r_A=\vec r_B + \vec r_{A/B}##, but ##\vec r_{A/B}## is equal to zero because they have the same origin, so the position measured from ##A## is equal to the position measured from ##B## II) For ##A##, velocity...
  2. M

    Find the fractional increase in inertial mass when an ice cube melts

    Summary: Apparently an ice cube gains mass when it melts So I'm asked to "Find the fractional increase in inertial mass when an ice cube melts ". All I've got off the top of my head right now is that a cube has energy = mc^2, and then when the cube melts, energy Q = (Heat of fusion)(m) is...
  3. H

    Entropy in a non inertial reference frame

    I know that the entropy of a system is the same in different inertial frames. Is this still the case for non inertial frames? For example, is the entropy of a body as seen from a rotating reference frame the same as the entropy seen from a fixed frame?
  4. T

    Is the Earth's frame considered inertial in a moving car?

    I have a really stupid question. Suppose I am in a car and the car is going around a loop. Yes, the Earth is not inertial -- it rotates -- but let me ignore that and, momentarily, designate the Earth as inertial. Now, we know the frame of the car is not inertial--the car is turning. We...
  5. J

    B Inertial & Gravitational Mass: When Do They Differ?

    Under what circumstances are they different?
  6. B

    Understanding Newton's First Law and Referential Inertial on a Moving Earth

    How we talk about referential inertial if the Earth always is in motion? Because if the Earth is in motion, everything is in motion with the Earth. So nothing is a inertial referential. How can we talk about Newton's First Law?
  7. O

    Energy in different inertial frames

    Lets neglect conservation of momentum and assume that all frames of reference are inertial. Now imagine three objects: the sun, the Earth and an asteroid. In the inertial frame of the sun, Earth and asteroid are flying towards each other ( velocitys v and -v). Now imagine you are standing at...
  8. TerranIV

    I Particles w/ 0 Inertial Mass Traveling Faster than Light?

    I was just curious if there were any known (theoretical) particles with zero inertial mass that don't travel at light speed. Is this even possible?
  9. sweet springs

    I Transverse inertial motion of rockets in acceleration

    Hello. I have a question on inertial motion transverse to gravity force, e.g. blocks of dry ice floating on the smooth and flat floor on Earth. For simple mathematics I explain my problem in Rindler case. Let a group of N rockets gather at origin (0,0,0,0) of a IFR and let them start...
  10. Buckethead

    B Time Dilation: Accelerating vs Inertial Frame

    This is probably common knowledge to relativity aficionados but at Example 7.3 in this paper: https://www.farmingdale.edu/faculty/peter-nolan/pdf/relativity/Ch07Rel.pdf I was surprised to read the author showing that a ship accelerating at 1g from rest for 1 hour and reaching a speed of...
  11. Opressor

    I Inertial Ref: Can Light Photons Be a Privileged Frame?

    Can light photons be considered as a privileged inertial frame?
  12. A

    What is and some explamples of inertial frame of reference ?

    I know this is a basic question, but I haven't understood deeply what a inertial frame of reference is, to be more specific, its relation with the first law of motion.
  13. Justin71

    Inertial force acceleration (vertical axis)

    Hi, How is the inertial force Fi (acceleration) when the system is vertical. I noted Fi_horizontal=m.a, Ff=mg.μ.cos(Θ) et Fg=mg.sin(Θ) .
  14. Adam564

    Centipede inertial frame problem

    Homework Statement A high-speed centipede in S’ is 10.0 cm long measured at rest in S’. A butcher in S holds two cleavers (A and B) 9.00 cm apart (measured in S). The centipede runs at such high speed v across a chopping block that the butcher measures the length of the centipede to be 8.00 cm...
  15. olgerm

    Angular speed that breaks a spinning body apart with inertial stress

    How to find the angular speed, on which a spinning hollow cylindrical body breaks due to inertial stress(force)? I found 2 sources(http://www.roymech.co.uk/Useful_Tables/Cams_Springs/Flywheels.html (last 2 equations) ...
  16. Pencilvester

    I Locally inertial reference frame problem

    Hey PF, I am working on a problem set, and one of the problems is proving that the Christoffel symbols vanish at the origin of the coordinates ##y^{\alpha}## given by the coordinate transformation: $$y^\alpha (x) = x^\alpha - x^\alpha_{(0)} + \frac {1} {2} (x^\mu - x^\mu_{(0)} )(x^\nu -...
  17. T

    Exploring the Math Behind Inertial Frames

    This question concerns inertial frames. I am aware that an inertial frame is one that is not accelerating. I am aware of an alternative definition: it is one on which no forces are applied. (Yes, they are the same thing.) I am also aware of the d'Alembert "forces" that appear when a frame is...
  18. L

    I Can two inertial frames differ by the speed of light?

    I know that special relativity is based on the postulate that an object that travels at the speed of light with respect to one inertial observer must travel with the speed of light with respect to all inertial observers. This postulate implies that no two inertial frames can differ by a relative...
  19. Manny46

    What happens with the puck in a non inertial board?

    I'm not being extremely exact here, but suppose there's a puck in a board where there's very little friction. Both puck and board are at rest. Suppose the board starts from rest to some decent speed, so there's definitely this acceleration, by virtue of which (and also less friction), puck...
  20. P

    I Are All Particle-Rest Inertial Frames the Same?

    According to special relativity, all inertial frames of reference are equivalent for descriptions of physical phenomena. Suppose that there is a free particle in free space. Observed in any of the frames, the motion of particle can be described by a velocity, and by Lorentz boost, one can get...
  21. Zahid Iftikhar

    I Inertial Frames: Constant Quantities?

    My question is about some physical quantities which two observers in two respective inertial frames will find the same. I wonder are there any such quantities? Some books say force, speed of light etc are constants for both the observers. Please guide me on this. Regards.
  22. N

    A Unlocking the Mystery of Mass: Exploring Electron Inertial & Heavy Mass

    In Abraham Pais book (which was first published in 1982), he states the following: "Quantum field theory has taught us that particles nevertheless have structure, arising from quantum fluctuations. Recently, unified field theories have taught us that the mass of the electron is certainly not...
  23. KFM

    Help Needed: Magnetic Inertial Hybrid Fusion Reactor

    Can anyone help with this please... Would the following work? Magnetic inertial Confinement Hybrid Fusion Reactor. Peeta Watt lasers are focused on the plasma in the equatorial plane of the multi mega amp plasma pulse within its’ torous geometry between the center post and the merging...
  24. J

    Position of particle in inertial reference frame

    Homework Statement The position of a participle in a fixed inertial frame of reference is given by the vector r = i(x0 + Rcos(Ωt)) +j(Rsin(Ωt))where x0, R and Ω are constants. a) Show that the particle moves in a circle with constant speed Homework Equations F = mv2/r The Attempt at a...
  25. P

    I Velocity of Particle vs Inertial Frame Velocity

    Hello all, This post is in reference to a previous homework post, found here: https://www.physicsforums.com/threads/show-that-f-gamma-3-ma.338744/ That thread is closed to further replies. Probably because it's nearly 10 years old. That thread is about deriving relativistic force from the...
  26. Swag ranger

    Acceleration in an inertial reference frame

    Homework Statement 3. (a) If an object's acceleration is zero in one inertial reference frame then is its acceleration zero in all other inertial reference frames? (b) If an object's velocity is zero in one inertial reference frame then is its velocity zero in all other inertial reference...
  27. jaketodd

    B Inertial Objects: Acceleration & Direction

    Are two objects, accelerating at the same rate, and in the same direction, considered inertial to one another? If so, I will post my resulting question. If not, it's safe to disregard this thread. Thanks, Jake
  28. Lee Sung Bin

    B Relativistic Physics: Gravitational & Inertial Mass

    In Newtonian mechanics, both gravitational mass and inertial mass is m. This principle is known as the principle of equivalence. However, I heard that in Relativity, gravitational mass is γm instead of m because total energy of the particle is γmc2. But in special relativity, it is widely known...
  29. C

    Understanding meaning of inertial reference frames

    Homework Statement Which of these situations describes you observing from an inertial reference frame? a. you are in the car of a train, seated at a table, and the train suddenly slows down b. you are in the car of a train, going north, and the train goes around a curve to go west c. you are in...
  30. G

    Inertial loads -- Sources of information needed

    I'm working with Aerodesign, and I want to study "Inertial loads" but I can't find books about the subject, do you know any? thank you
  31. B

    I Inertial frame of freely falling body

    A freely falling body (falling in earth) accelerates with time. However, an object inside the body remains at rest (if it was initially at rest) or moves with a constant velocity if it was initially moving with constant velocity. In other words a frame fixed to the body is an inertial frame...
  32. Wilson129246

    Inertial Integrity in Space Flight: Questions Answered

    Maybe i should pose this query in a different area, but since it involves basic physical laws of motion... Space flight? I know this should be obvious enough but i was wondering how a shuttle is capable of maneuvering once in an area with which gravity and atmosphere play too little a part on...
  33. S

    What is the force acting on a rotating body in a non-inertial frame?

    Hello! The angular velocity in the non-inertial frame of a rotating body of mass m is ##\Omega## and I need to find the force acting on the body (in the non-inertial frame associated with the body). In the book they say (without any derivation, they just state it) that the force is...
  34. M

    Inertial Dampers: Solutions for Sci-Fi Concepts Like Iron Man & Spaceships

    I would like to know what ways are there to get rid of the inertia problem when it comes to sci-fi concepts such as Iron Man and spaceships. I'm actually more interested in how could it be possible for a spaceship to accelerate to a very high G without causing its inhabitants a mass concussion...
  35. J

    Inertial and Gravitational mass - Assertion Reason

    Homework Statement [/B] Homework EquationsThe Attempt at a Solution I think the two masses , inertial and gravitational are equivalent and because of this fact , the ratio of the two masses is one . The correct option should be 1) . But the answer given is 3) i.e A statement is true and R...
  36. J

    Is free fall NOT the same as floating in space?

    For many, many years (don't ask), I've been running into the classic example of the local reference frame: the man in the box who can't tell if he's floating free in space, or falling into a gravity well. It occurs to me that if one is in a falling box, a mass released at the top of the box...
  37. C

    Body Force vs Inertial Force: What's the Difference?

    Hello everyone. This is my first time on the physics forum, but I think I'm going to be a regular here. I was reading a paper that outlined various ways to approach solving dynamic problems. The first approach outlined by the author is D'Alembert's principle of virtual work. In describing...
  38. C

    Forces in inertial and non-inertial frame of reference

    Imagine such situation: A bus is moving at constant speed, a man is standing on the bus and is not holding to anything - he is simply standing. Now, the bus starts breaking with constant negative acceleration and so the man will change his relative position due to the force of inertia. Now...
  39. Ibix

    I Transforming to Local Inertial Coordinates

    I've been playing around a bit with the Kerr orbit program I wrote, and have been thinking about ways to set the initial conditions. One thing I'd like to be able to do is specify a launch from some event in terms that would be convenient for an observer at that event with some given...
  40. A

    Inertial frame where rods have same length

    Homework Statement I was re-reading my old Relativity book (by Rindler) and taking a look at some of the problems. He asks: Using a Minkowski diagram to establish the following result: Given two rods of rest lengths ##l_1## and ##l_2 (l_2 < l_1)##, moving along a common line with relativity...
  41. G

    B Inertial and gravitational mass

    Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory? (since it also cannot be explained as a neccessity by the anthropic principle)
  42. D

    IC Engine Connecting Rod Mass Moment of Inertia Measurements

    Does anyone know of a source, on the Internet preferably, for component inertial data for a real IC engine? In particular, what I'd like to obtain (for some real engine, any engine) are these items: 1. Piston weight (including wrist pin) 2. Cylinder bore dimension 3. Connecting rod length...
  43. nomadreid

    I Understanding Special & General Relativity: Inertial vs. Gravitational Frames

    I know this is a naive question that has almost certainly been brought up numerous times before, but my search abilities seem not to be sufficient for finding a good answer, so if anyone just refers me, that would be fine. The question: Special relativity concerns comparisons between pairs of...
  44. Altair Tans

    Inertial Current: Electron Movement & Current Generation

    Are the electrons of a conductor so loosely bound that just moving a current might give rise to a tiny bit of current owing to electron's inertia??
  45. R

    Newton's first law of motion and Inertial Systems

    I have just begun my journey in Classical Mechanics with the book "An Introduction to Mechanics" by Kleppner and Kolenkow. I find myself stuck at Newton's first law. The book presents Newton's first law as follows: "Newton's first law is an assertion that inertial frames exist." The book also...
  46. F

    I Inertial & non-inertial frames & the principle of equivalence

    One particular form of the equivalence principle states that The laws of physics for freely falling particles in a gravitational field are locally indistinguishable from those in a uniformly accelerating frame in Minkowski spacetime My question is, does one arrive at this conclusion from a...
  47. parshyaa

    Question about inertial and non inertial frames

    Suppose a person A is standing in a bus and bus is accelerating forward then when a person B standing outside observes A he see that A is accelerating in forward direction then there must be a force acting on him which is making him accelarating(because Newtons first law holds in Earth's frame)...
  48. parshyaa

    Question related to inertia and non inertial frame

    Suppose a person is standing in a bus, moving with constant velocity and then driver applied the breaks and the person standing moved forward as if something pushed him from behind Whats the reason behind this Is it because bus has become a non inertial frame and we have to add psuedo forces to...
  49. S

    Inertial Reference Frame Proof

    Consider a specific reference frame (0XYZ) attached to Earth. A point (origin) being selected, coordinates are ascribed along with a vector basis. This reference is non-inertial because it is locked to Earth and the acceleration of Earth is not zero. Suppose upon rising one morning I felt...
  50. T

    B Electric+Magnetic Force Between a & b Charges: Inertial Frames

    Let's assume that a and b charges are moving. now in our lab frame there will be a electric+magnetic force whereas in a rest frame of either of the charges, there will be only an electric force. So, two inertial observers will measure different forces?
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