Inertial Definition and 500 Threads

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. P

    Gravitational and inertial mass

    In physics as a general discipline, there are 2 types of mass gravitational and inertial which have different definitions but experimentally they have turned to be extremely similar, 1 part in 10^12. Moreoever, general relativity predicts they are equivalent. They are all measured by an observer...
  2. L

    Gravitational mass & inertial mass

    Hey, first time here. I'm currently reading up on Physics, preparing for a selection test by myself. I need some help in understanding Newton's gravitational mass and inertial mass. Are they different? I read that there are some difference, and these masses ARE slightly different. Any reason...
  3. J

    Transformation to a local inertial Frame

    So I've been working on this problem. I am given the metric in Kruskal coordinates, so ds^2=32M^2exp(-r/2M)/r(-dT^2+dX^2)+r^2(dθ^2+sin^2(θ)dΦ^2) And the path of a particle is X=0 T=λ θ=π/2 Φ=0 And the path of the observer is X=-1/2*T+1/2 θ=π/2 Φ=0 And I am asked to find the 3...
  4. S

    Measuring Inertial Mass: Force, Acceleration and Mass

    I was wondering, how is it that scientists measure inertial mass. I presume they use F=ma, and thus the mass of an object would be measured by applying a force on an object and finding out the resulting acceleration. Getting acceleration is simple, but how can they measure the force? Then if...
  5. I

    What is the approach for solving a non-inertial pendulum problem?

    Hi, I have this practice problem I'm trying to figure out. A pendulum 80 cm in length has a mass of 0.4g is suspended on the roof of a truck accelerating at 2.6m/s/s. Find a) the horizontal deviation of the mass; b) the tension in the cord. For a, I know the answer is 20.6cm but I...
  6. A

    Inertial Reference Frames- circular?

    My textbook basically defines an inertial reference frame as follows: If you have an object O that has no forces acting on it, and there is a reference frame R where the acceleration of O with respect to R is zero, then R is a inertial reference frame. This to me seems circular. How does one...
  7. G

    Calculate Inertial Constant K I for Sphere + 4 Disks

    I = kMr 2 Where M is the mass of the flywheel, r its radius and k is its inertial constant. Can I calculate my own inertial constant( a sphere + 4 disks around the sphere) Thanks Help will be appreciated
  8. P

    Inertial mass, invariant mass and the photon?

    In some cases, inertial mass does not equal invariant mass? What is the relation between the two? So the photon can have non zero inertial mass but always 0 invariant mass?
  9. S

    Special Relativty and Inertial Reference Frames

    Hi - I've just started having lectures on special relativity at uni. We were talking about inertial reference frames and how these can be characterised by the facts that: 1) They move relative to one another with constant velocity, and 2) Newton's laws operate in inertial reference frames...
  10. K

    Inertial frame of reference help

    In an inertial frame of reference, a series of experiments is conducted. In each experiment, two or three forces are applied to an object. The magnitudes of these forces are given. No other forces are acting on the object. In which cases may the object possibly remain at rest? The forces...
  11. L

    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...
  12. F

    Special relativity and inertial frames of reference

    i hope u can answer these ? for me please 1) how does einstein's special theory of relativity and inertial frames of reference explain and predict the behaviour of natural phenomena (weather)? 2)explain the conservation mass -energy as applied in special relativity? 3) what is the...
  13. M

    Speed of light in an inertial frame

    Does the speed of light for an observer falling into a black-hole remain the same?
  14. B

    Same experiment performed in different inertial reference frames

    under which conditions we could say that the same experiment is performed in different inertial reference frames. I have formulated for myself the following answer: We say that observers from two inertial reference frames perform the same experiment if the physical quantities they measure are...
  15. S

    What if inertial mass did NOT = grav. mass?

    What if inertial mass did NOT equal gravitational mass? How would our normal daily existence be different? Most interesting and creative answer wins ! [Edit: This is intended to be a fun question to answer, but I'm hoping to learn something quite serious from it. The force of...
  16. I

    Inertial Mass Propulsion? Feedback wanted.

    I have had this idea in my head for years and I want to know once and for all if it will work or not. I understand that a flywheel gains in mass when it spins. If this is true, is my thinking below correct? Any feedback would be appreciated! Inertial Mass Propulsion: I am going to try to...
  17. M

    Another Inertial ref frame q :-(

    It's not that I don't believe that all i.r.f.'s are on an equal footing, it's just that I can't seem to get that to square with the following thought experiment, undoubtedly 'cause I'm getting lost in my own undies here, and I need help getting a handle on this. Suppose you have a universe...
  18. L

    I can't understand inertial reference frames

    Hi, Please help me, I can't make head or tail of the concept of an inertial reference frame. What is an inertial reference frame? In what fundamental way does it differ from a noninertial reference frame if all motion is relative? Thanks for your help. Molu
  19. A

    Interaction Energy how does it transform between inertial frames?

    Energy is not an invariant quantity between different frames of reference. For example a particle having a kinetic energy in one frame has a zero kinetic energy in another frame. But what about interaction energy? If I know the interaction energy between 2 particles in one frame, how can I...
  20. J

    Inertial frames in special relativity

    What is used to define an inertial frame in special relativity? Do I need to take one of the postulates as defining an inertial frame? What is bothering me is that I used to use Newton\'s first law to define inertial frames (a freely moving object will have a constant velocity). This can...
  21. Y

    Inertial Frames distinguished by proper times

    A first spaceship S1 departs from Earth and quickly accelerates to a velocity V = c/2. S1 travels the shortest path (dead heading) toward a distant planet Alpha so that it arrives in 20 years as measured by a clock on S1. One year after S1 is launched from Earth as measured by a clock on the...
  22. Amith2006

    Simple pendulum, and inertial and gravitational mass

    Sir, A simple pendulum has a length L. The inertial and gravitational masses of the bob are m1 and m2 respectively. Then the time period of the simple pendulum is given by T = 2(pie)[m1L/m2g]^(1/2) {Read as 2 pie root m one L by m two g) My question is that the...
  23. V

    Is momentum conserved in all inertial frames of reference?

    hi, in the case of elastic collision of two balls in constant speeds, if we took the origin in the center of of one of the balls, so the speed of the origin ball will be always zero, and the second ball will has the speed of v befor the collision and -v after the collision. so how the...
  24. E

    How do I apply inertial reference frames to a puck's path?

    when I read what inertial frames I understand and it make sense but unfortunately when I try to apply what I understood on that question ,I can't illustrate these frames. Please help. question is that: I am standing on a level floor at the origine of an inertial frame ( S) and kick a...
  25. R

    GR: Inertial Systems & Direction Changes of Motion

    When a canon shoots a ball straight up (one dimension), the ball only accelerates as long as the nongravitational force of the canon acts on it. After that, the ball decelerates in the gravity field until the point it turns back and accelerates in the opposite direction as it falls back on...
  26. R

    Locally Inertial Coordinates: Spacetime Points & Freely Falling Particles

    Locally inertial coordintates in GR refer to spacetime, not only to space, right? Are they only defined for events, for spacetime points, so that when a particle is freely falling it passes through infinitely many such locally lorentz frames? But if so, how can we say that the particle runs...
  27. T

    What is the pressure of gas inside an inertial fusion pellet?

    I asked one of the professors in the nuclear engineering department recently how inertial fusion could be a viable energy source if so little matter was fused. He told me that I would be suprised and said that I should do the calculation myself. I found the volume of the pellet, but now I have...
  28. S

    Rotational Inertial and Torque question

    Can anyone help me out? :smile: The top has a moment of inertia of 0:0002 kg.m2 and is initially at rest. It is free to rotate about a stationary axis AA'. A string, wrapped around a peg along the axis of the top, is pulled in such a manner as to maintain a constant tension of...
  29. S

    Need help with torque and angular inertial problems

    Figure 10-43 shows particles 1 and 2, each of mass m, attached to the ends of a rigid massless rod of length L1 + L2, with L1 = 19 cm and L2 = 79 cm. The rod is held horizontally on the fulcrum and then released. a.What is the magnitude of the initial acceleration of particle 1? b.What is...
  30. M

    Is Your Classroom an Inertial Frame of Reference?

    Are you in inertial frames? hi, today my friend ask me 2 simple questions, too shame i cannot answer him...so i post it here: is the classroom an inertial system ?? Earth is rotating around the sun - so ...can still consider as inertial ? 2. If u working in laboratory to find so physics...
  31. M

    Is momentum conserved in all inertial frames?

    and is the momentum of a particle the same in all inertial frames? Thanks for any help
  32. A

    Inertial Disk Lab: Physics 11 H Experiment

    Ok, in my Physics 11 H class we did a lab with an inertial disk (a disk with a hub in the center, a string is attached to the hub like a huge half a yoyo where the yoyo is stationary and weights are the fingers falling down) and i need to be able to calculate the tension in the string for...
  33. F

    Lab on measuring the inertial mass

    Ok we just did a lab on measuring the inertial mass. This is going to be really hard for me to explain but i'll try. Anyways here's the problem the gravitation masses are given to us.The are 100g, 200g, 300g and 400g. We also have to use ticker tape and we ended up finding the acceleration by...
  34. B

    Conservation of Energy in different inertial frames

    today my dynamics lecturer illustrated a situation to us where energy did not appear to be conserved. The situation involves observing the motion of a mass sliding down a slope, height 'h' above the ground from rest initially in the rest frame, we see; initially, PE = mgh KE = 0...
  35. W

    Graviton Theory: Inertial vs Gravitational Mass

    gravitons ?? is the inertial mass proportinal to the gravitational mass in the graviton theory of gravitation ? I ask this because I can see easily how GR imply that the two masses must be equal since spacetime curvature acts at everypoint in the body. But with gravitons I can't understand how...
  36. C

    What is the Correct Calculation for the Inertia Tensor in a 2D Rotation?

    my homework problem deals w/ rotation in x-y plane. so the tensor is only 2d. inertial tensor still seems obscure to me... my question for now is purely mathematical. assuming the basis are (x,y). I calculated the components of I, is the following correct? I_{xx} = m_i y_{i}^{2} I_{yy} = m_i...
  37. M

    Speed of light measured the same by all inertial observers?

    What is the speed of light measured the same by all inertial observers?
  38. ?

    Frames of reference & Inertial frames

    i've just started studying these but unfortunatley I've been unable to get my hands on the textbook, and my lecturer is... not that great :frown: Could somebody explain what these are to me? I have little to no idea about them as of now... maybe a few sample questions too? That would be a...
  39. Reshma

    Inertial & non-inertial frames

    Could someone explain me in detail the differences between an inertial reference frame and a non-inertial reference frame? Are inertial frames restricted to Euclidean space?
  40. H

    Why does the stick in a moving frame shrink vertically?

    dear friends, i have one problem regarding the inertial frames.it is said that freely falling elevator satisfies the above property.if there are two particles inside the elevator the distance betn. them will remain same as long as the distance is small.but when the distance betn. the paricles...
  41. S

    Is a Skydiver at Terminal Velocity an Inertial Reference Frame?

    1) Which object provides an inertial frame of reference? a. the tip of the moving second hand of a clock b. a rock thrown vertically upward c. a pendulum swinging with no air resistance d. a skydiver falling at terminal velocity At first I thought c might be correct, but now I am...
  42. D

    How Do We Determine Proper Inertial Frames of Reference?

    how do you determine if something is a proper inertial frame of reference? the Earth is but a car isnt? you can feel a car accelerate, even though you are in it, but you can't feel the Earth accelerate as it changes directions in its orbit.. is there a poitn after which you don't feel...
  43. G

    Spin-1 particles: Intrinsic Inertial Platforms.

    The simplest Stern-Gerlach spin-1 transition is the +S -> +T -> +S transition. The expression defines two events: 1) Polarization event of the +S state when passing to the +T state, +S -> +T, from the field free region to the field/gradient volume of the Stern-Gerlach T segment. Here we...
  44. K

    Inertial reference frames

    I can make a local inertial reference frame in a gravitational field by creating a frame that is small but close to the source of curvature of space-time. Alternatively I can make a local inertial reference frame by creating a frame that is large but a long distance from the source of curvature...
  45. W

    Permittivity in inertial reference frames

    Suppose 2 inertial frames with relative relativistic velocities. To discuss phenomena in other frame, we need to use Lorentz Transform for length and time. I got question: do we have to also use LT to talk about permittivity and permeability of other IRF? This seems strange. Permittivity has...
  46. Hamish

    Electron beams and an inertial frame problem

    I wasn't sure whether to post this in the classical or relativity section. While pondering something I found an embarrassing gap in my knowledge. I can't quite get my head around this problem and I need a fresh perspective. Consider two beams of electrons moving parallel to each other. The...
  47. 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?
  48. 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...
  49. S

    Inertial and gravitational mass

    What's the difference between inertial mass and gravitational mass?
  50. P

    Inertial mass of a stressed body

    I was wondering if anyone out there knows how to do Exercise 5.4 on page 159 of "Gravitation," by Misner, Thorne and Wheeler? It goes like this - let d^jk = Kronecker delta Consider a stressed medium in motion with ordinary velocity |v|<<1 with respect to a specific Lorentz frame (a) Show...
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