# What is Inertial reference frame: Definition and 41 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. ### Kinetic energy in center of mass reference frame

Here is the relevant chapter. Suppose we have two masses ##m_1## and ##m_2## interacting via some force, and two reference frames, ##S## and ##CM##. The ##CM## frame is the center of mass reference frame. The origin of this reference frame is at the location of the center of mass of the system...
2. ### Calculate center of rotation of monocopter

I want to calculate center of rotation for monocopter, from inertial reference frame,earth. One case when fly in the air in one steady height/place and second case is in free space,then has rocket engine instead fan. I draw forces what I think that must exist. m=2kg Ft(thurst)= 100N ω=500RPM...
3. ### Torque about an accelerating point

The total force acting on the pulley is zero so: F=mg+T1+T2 (1)Analyzing the torque and angular acceleration about the actual axis of rotation, the axle of the pulley, gives: τnet=T1R−T2R=Iα (2)If we analyze about point P, the right edge of the pulley where T1 is applied, we get...
4. ### I Relative Motion & Local Frame’s Position - when projecting components

Does the position of the origin for the body’s rotating coordinate frame 1) stay fixed to the moving body or 2) does it stay fixed to the inertial frame, yet still able to rotate as the body rotates with the only restriction that it cannot translate with the body i.e. only affixed at the...
5. ### Why do particles in a falling coach get closer together?

As widely separated particles within a large enclosed space are differently affected by the nonuniform gravitational field of Earth, to use the Newtonian way of speaking, two particles released side by side are both attracted toward the center of Earth, so they move closer together as measured...
6. ### I Reference frame vs coordinate chart

Hello, here on PF I've seen many threads about the concepts of 'reference frame' and 'coordinate system'. In the context of SR my 'envision' about the concept of 'frame of reference' is basically the 'rods & clocks latticework' as introduced in the book Spacetime physics (Taylor, Wheeler)...
7. ### 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...
8. ### 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?
9. ### 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 -...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### Momentum and Inertial Reference Frame

Homework Statement At the roller rink, two 20-kg girls accelerate toward each other until they are each moving at 2.7 m/sin the Earth reference frame. They then collide stomach-to-stomach, grab on to each other, and fall to the floor. A. Calculate the magnitudes of the momentum of each girl...
14. ### I Earth as Inertial Ref. Frame: Test Relativity's Precision

Special relativity is one of the most tested theories in physics. A central postulated of SR is that the speed of light is the same for all observers in inertial reference frames, and this leads to time dilation and the other effects that have been tested with a high degree of precision. We...
15. ### B Distinguishing inertial reference frames

As described in Wikipedia as well as this entry http://physics.stackexchange.com/questions/172739/is-the-lay-explanation-of-the-equivalence-principle-wrong, "being at rest on the surface of the Earth is equivalent to being inside a spaceship (far from any sources of gravity) that is being...
16. ### Acceleration in a non inertial reference frame

Homework Statement A platform rotates with ##\omega=10## rad/s around ##z##-axes. A ball is connected, with a yarn to ##z##. Its distance to the axes is 15 cm and it rotates with ##\omega=10## rad/s. There isn't friction between platform and ball. Suddenly, the angular velocity of the...
17. ### Invariance of Acceleration in Inertial Reference Frames

Claim: The acceleration (both direction and magnitude) for any object is the same in any inertial reference frame. Is this claim true? I think it is, but someone mentioned to me that time may be an issue as it's not agreed upon in all inertial reference frames. I'd appreciate any references...
18. R

### What are inertial reference frames?

I just read about the two postulates in the theory of special relativity. And the first one says that the laws of physics are the same in all inertial reference frames. Can anybody explain me what does it mean?!
19. ### What is a pseudo-force and how does it relate to non inertial reference frames?

So I was told that a pseudo-force acts on a body when its's motion is analysed with respect to a non inertial reference frame. I'm a bit confused. Does that mean the reference frame is accelerating with respect to the body, or with respect to the earth? And why does there have to be any sort of...
20. ### Inertial Reference Frame Locally

Why can we not CHOOSE a reference frame locally and treat everything inside of it as an inertial reference frame. For example in a classroom, the classroom is moving with the Earth and so is a ball rolling down the class. Because they are both equally moving due to the Earth's rotation, why...
21. ### What exactly is an inertial reference frame?

Due to my job and other classes, I've been studying ahead of my class by myself to not fall behind and I'm not sure if I'm oversimplifying this in my head and not really grasping the idea. Newton's First Law of Motion states that an object with a net force of zero stays in constant motion (or...
22. ### Can Earth be considered an inertial reference frame?

hi guys, i have a basic question on special relativity.. if the inertial reference frame denotes the frames that holds up the Newtonian 1st law, then can Earth be an inertial frame? i mean it changes direction of velocity as it moves in the orbit around sun, so its not in constant velocity ...
23. ### Can inertial reference frame have different sizes at least in theory?

hi can inertial reference frame be in different sizes at least in theory? i mean that can there be two different frames of reference in same place at same time, where the observer in both frames observes physical laws to be normal in their own frame of reference, but the other frame appears to...
24. ### Generalized momentum and Hamiltonian over a non inertial reference frame

Hi there. I need help to work this out. A particle with mass m is studied over a rotating reference frame, which rotates along the OZ axis with angular velocity \dot\phi=\omega, directed along OZ. It is possible to prove that the potential (due to inertial forces) can be written as: V=\omega...
25. ### Basic question about inertial reference frame

I have no background in relativity. Recently I started reading some introduction to special relativity in Griffith's EM book, where he vaguely defined an inertial reference frame as one in which Newton's first law holds. Now according to this definition, does such frame exist in nature? On...
26. ### Non inertial or inertial reference frame?

Homework Statement Specify and explain whether the following is an inertial or non-inertial observer: An observer is placed on a rock between Andromeda and the Milky Way. Homework Equations N/a The Attempt at a Solution So here is my understanding, the observer would be situated...
27. ### Magnetic force in a moving inertial reference frame

A charged particle is placed next to a current-carrying wire. The wire produces a magnetic field, but if the particle is at rest, the field exerts no force on it. However, in a different inertial reference frame moving at speed v parallel to the wire, the particle is seen to be in motion, and so...
28. ### Torque in a non inertial reference frame

Hi, This is partly inspired by the questions in the thread about normal forces on a cornering car but I thought I'd post here instead of mix that thread up with my question. So suppose we have a biker leaning into a corner. There are the normal force and the force of friction which act at the...
29. ### 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...
30. ### 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...
31. ### 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...
32. ### Inertial reference frame for 2&3 law

Does the concept of Inertial reference frame also applicable for 2nd & 3rd law of motion?
33. ### 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...
34. ### Is Poincare Symmetry Fundamental to Relativity as Proposed by Einstein?

I have heard the following oppinion: Whether a reference frame is inertial is completely determined by whether Newton's laws are applicable for particles moving at low (that is, nonrelativistic) speeds in that reference frame. Do you agree with it?
35. ### Defining Inertial Reference Frames in General Relativity

How can you have an inertial reference frame in which a body can remain at rest or move with constant velocity unless you postulate the disappearance of the universe? In the Michelson Morley experiment the Earth is not moving with constant velocity, it is accelerating. So the postulates of...
36. ### Newton's Laws and Inertial Reference Frames

does an object with constant acceleration follow Newton's laws? with constant velocity? a stationary object? i think the last two are true, but I'm confused whether a constant acceleration (m/s/s) of whatever still applies to an inertial frame or is a noninertial frame? because in a sample...
37. ### How Do Moving Frames Affect the Observation of a Puck's Path?

I am standing (yes, the question actually goes like this!) on a level floor at the origin of an inertial frame S and kick a frictionless puck due north across the floor. a.) Write down the x and y coordinates of the puck as functions of time as seen from my inertial frame. (use x and y axes...
38. ### Possible webpage title: Defining Inertial Reference Frames in Classical Physics

Hello, Every definition of an inertial reference frame that I have read stated that it is a frame in reference in which Newton's laws are valid. But is it possible to define it in this way: it is a coordinate system that is not accelerating relative to some absolute reference point. Is there...
39. ### Basis for the postulate that all physics is the same for all inertial reference frame

SR is based on the postulate that all physics experiments yield the same results regardless of inertial reference frame? What was Einstein's basis for this assumption? What thought process did he go through to come to that conclusion? How could he know the speed of light was the same...
40. T

### What is an inertial reference frame?

I am not really sure I have the concept of an inertial reference frame down, can anyone help me?
41. T

### On The Definition Of An Inertial Reference Frame

There are various definitions of an inertial reference frame out there, but only one is really accepted by the physics community. In some places, you will see an inertial reference frame defined as a a reference frame in which Newton's law of inertia is valid. In some places, you will see...