Frame Definition and 1000 Threads

A vehicle frame, also historically known as its chassis, is the main supporting structure of a motor vehicle to which all other components are attached, comparable to the skeleton of an organism.
Until the 1930s, virtually every car had a structural frame separate from its body. This construction design is known as body-on-frame. By the 1960s, unibody construction in passenger cars had become common, and the trend to unibody for passenger cars continued over the ensuing decades.Nearly all trucks, buses, and most pickups continue to use a separate frame as their chassis.

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  1. F

    Motional EMF in the frame of a moving wire

    When a magnetic field is moving (moving magnet) while a wire isn’t---in the reference frame of the wire, there’s no known magnetic force/effect on the wire before the introduction of motional emf and relativity. If viewed in the reference frame of the magnetic field instead where the wire is...
  2. JD_PM

    I Understanding how to derive the cross-section formula in the CoM frame

    We work in natural units. Let's assume in this post that the differential cross-section of two particles that, after collision, yield ##N## particles is given by the following formula: $$d \sigma = (2\pi)^4 \delta^{(4)} (\sum p'_f - \sum p_i) \frac{1}{4 E_1 E_2 v_{rel}} \Pi_l (2m_l) \Pi_f...
  3. LCSphysicist

    Trajectory in a non inertial frame

    Well, make the center of the polar coordinates at the center of the turntable, so put r along the ro initial. I am well known that to someone who is rest on the turntable, the equations will be the follow: dr/dt = ro - vt If the turntable route with angular velocity w, dtheta/dt = -wt We...
  4. A

    Collision time between two rockets in one rocket's frame....

    While attempting this question , velocity of ##B## wrt ##A## ,##u'_x=\frac{u_x-v}{1-u_xv/c^2}## where ##u_x=-0.6c,v=0.8c## comes out to be ##-0.945c## (approaching).. The distance between ##A## and ##B## seen by ##A## at ## t=0## is ##d=\sqrt(1-.8^2)4.2×10^8## comes out to be ##252*10^6m##...
  5. L

    Momentum and energy in Center-of-Momentum frame

    To my mind because one particle has momentum ##\vec{p}## and the other one ##\vec{0}##. It is for instance necessary to find reference frame where one momentum will be for instance ##\frac{1}{2}\vec{p}## and the momentum of other particle should be ##-\frac{1}{2}\vec{p}##. So it is necessary to...
  6. Tony Hau

    Derive the equation of effective force on a rotating frame about Earth

    In my textbook, the effective force of a particle on a rotating frame is given as below: The diagram is: What I do not understand is the expression for Rf dotdot, which is given as below: According to the book, an arbitary vector Q can be expressed as: So Rdotdot w.r.t fixed frame can be...
  7. Robert Friz

    I Frame Dragging Around Spinning Black Holes: Implications

    Frame dragging around a spinning black hole is generally accepted in cosmology. Does the frame dragging result solely in space-time rotating forever around the black hole, or does frame dragging ultimately result in space-time vectoring towards and into the black hole? An additional question...
  8. K

    I CM frame kinetic energy for a molecule

    Hello! When the kinetic energy of a molecule is written in its CM frame we get the formula attached. The first term is the kinetic energy of the CM frame with respect to the lab frame, the second term is the kinetic energy associated with the distance between the nuclei and the last term is the...
  9. Arman777

    I Comoving Reference Frame in Cosmology

    In cosmology, the preferred reference frame is the comoving rest frame. I am trying to understand why we are using this frame and not another one. The only reason I could come with is this. Since the expansion of the universe is homogeneous and isotropic it seems our best choice is using the...
  10. cianfa72

    I Speed of Light in Vacuum in Non-Inertial Frame

    Hi, I read various threads in PF about the concept of invariant speed and the speed of light in vacuum that in our universe happens to be the same as the 'invariant speed'. My doubt is about the speed of the light in vacuum as measured from a non-inertial frame (basically in the context of SR...
  11. R

    I Lab frame and accelerator frame

    In the file I present below,it shows a way to calculate luminosity in boost frame when crossing angle exists.I can't understand why luminosity calculation is done in boost frame instead of lab frame where calculations are much easier.I also have difficulty understanding lab frame,accelerator...
  12. T

    A Simple question on the derivative of base frame

    I apologize: despite my verbosity, this is, I hope, a simple question.) Consider the following relationship between a rotating reference frame and an inertial reference frame (both Bold), through a rotation matrix: (the superscript is to designate the rotating frame e(1) and the I is for the...
  13. ruivocanadense

    I Does Conservation of Momentum & Energy Hold in the C.O.M. Reference Frame?

    We know classical equations fail to follow conservation of momentum and energy when we are dealing with speeds closer to the speed of light. But does it fail in the center of mass reference frame of a system?
  14. R

    B Moving Faster Than Light: Are There Symmetrical Rules?

    Would it be correct to say, that we are moving away from stars at the edge of the universe, at the same rate that these stars are moving away from us? I am relating to stars that are moving in relation to us, at a speed that is faster than the speed of light. Is the symmetry that maintains that...
  15. M

    I Special Relativity & No Special Inertial Frame of Reference

    As per special theory of relativity, no inertial reference frame is special! If a spaceship is moving at 100 m/s, no one can conduct an experiment to determine whether it is moving at 100 m/s or the rest of the universe is moving to the opposite direction at -100 m/s, if I understand the...
  16. E

    Which inertial frame is used when resolving toward the centre

    For simple circular motion it is common to resolve forces toward the centre and relate this to centripetal acceleration, provided that the current reference frame is inertial. However where would such a coordinate system be positioned? Since it requires one axis passing through the line...
  17. PeterDonis

    I Earth-centered frame with Earth-Sun line fixed

    I have seen plenty of references to Earth centered inertial frames (axes fixed with respect to the stars) and Earth-centered Earth fixed frames (axes fixed with respect to the Earth, rotating at the Earth's angular velocity of rotation with respect to the stars). Does anyone know of a reference...
  18. T

    1st Law of thermodynamics : moving reference frame

    I'd like to apply the 1st law of thermodynamics in a reference frame (RF) moving with constant velocity. We have: ##\Delta{}E = E_{in} - E_{out}## I am limiting myself to rectilinear motion. Suppose we are in a RF moving with a constant velocity ##V##. Let the system consist of a mass ##m##. The...
  19. Saptarshi Sarkar

    I Speed of Light in Inertial Ref Frames: Photon Perspective

    According to the 2nd postulate of Special Relativity, speed of light in vacuum is the same in all inertial reference frames. If I take a beam of photons and see the other photons in the beam from a frame of reference of a single photon, do they look stationary or moving at the speed of light...
  20. Kermit_the_Phrog

    Simple Canon Question (Conservation Of Momentum): Frame of Reference

    Since Pi = Pf, 0 = MbVbg + McVcg I just need to express Vbg in terms of Vbc and Vcg (that is, I need to express the velocity of the ball relative to the ground in terms that I know/want to solve for): by reference frames: Vbc = Vbg + Vcg so Vbg = Vbc -Vcg Now I can sub in and solve 0 =...
  21. Athenian

    [Special Relativity] - Finding Angle θ as Measured in Frame S

    Below is the attempted solution after researching the contents available on Introduction to Electrodynamics by Griffith. To begin with, I defined the rod as having a length of ##l'## at rest in frame ##S'##. Thus, in frame ##S'##, the height of the rod is ##l' sin(\theta ')## and its horizontal...
  22. lLehner95

    Find the photon energy in the center of mass frame and vice versa

    I tried to use the Lorentz transformation: ##E^{*}_{\gamma }=\gamma _{cm}E_{\gamma }-\beta _{cm}\gamma _{cm}p_{\gamma }## We have a photon, so it becomes: ##E^{*}_{\gamma }=\gamma _{cm}E_{\gamma }(\beta _{cm}-1)## Unfortunately, the solutions say that the correct way is to use the inverse...
  23. S

    B Length Contraction in Accelerated Frame

    I was wondering, would there be a length contraction (or expansion) in the z and y axis' if an object was accelerating in x axis? I know that in special relativity there is no deformation in the y and z axis' if the object is moving in the x axis. I was looking a this paper for clarification.
  24. Like Tony Stark

    Acceleration for a non-inertial reference frame

    Well, first a wrote the equation for acceleration in non inertial systems. ##a_I=a_o+\dot \omega \times r+\omega \times (\omega \times r)+2(\omega \times v_{rel}) +a_{rel}##. Then, ##a_o=0## (because the system doesn't move), ##a_i=0## (because it is measured from the non inertial system)...
  25. kepherax

    Moment of Inertia of a Rectangular Picture Frame

    https://www.physicsforums.com/attachments/250905 I know the answer, but am not certain how they got Lsin(angle) for R?
  26. N

    How are counts per frame calculated in CCD for spectrometry?

    I don't know if this is the appropriate forum for it. But I'd like to understand the concept of counts per frame in CCD in visible or IR spectrometry. If the exposure is say 200 ms and there are 12 frames. What is the counts per frame? Do you multiply 200ms by 12 frames to come up with 2400...
  27. Like Tony Stark

    Acceleration acting on a block lying on a wedge (non-inertial frame)

    I have some difficulties trying to understand non-inertial frames. I have problems to notice the acceleration in these cases, from an inertial reference frame and from non inertial refrence frame. Consider the first case, if I'm on the wedge, I see that the block doesn't move so there's no...
  28. 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...
  29. glmhd

    I How to make something independent of the coordinate frame?

    In page 49, chap 8 of the book "classical mechanics point particles and relativity" of Greiner, there is the following sentence: "In order to become independent of the coordinate frame, a set of orthogonal unit vectors is put at the point of the trajectory of the mass point given by ##s##."...
  30. L

    Rotational Frame Transformations

    Consider a rotating disk with the center at the origin of a stationary Cartesian coordinate system, (x, y). At t = 0, on the circumference of the disk, someone/something shoots a particle with constant velocity components Dvx, Dvy (where the D indicates the rotating disk). Also at time t=0...
  31. 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?
  32. x-vision

    B Reference frame symmetry in Special Relativity

    Hello, I have a couple of questions related to reference frames in Special Relativity. Let's consider a rocket that is inertially moving towards a star with a relative velocity 0.9c. I'd like to look at this example from both the rocket's and the star's perspectives. In the reference frame of...
  33. M

    B Question about the rest frame of a photon

    [Mentors’ note: this thread was split from the FAQ at https://www.physicsforums.com/threads/rest-frame-of-a-photon.511170/] I am not an expert! As I understand it, Einstein considered, what a guy standing in a photon will experience if he look at his watch. My understanding says, that the...
  34. E

    B Finding the length of a metre stick from a moving frame of reference

    Suppose we have a stationary metre stick with one end positioned at the origin of a stationary frame of reference, pointing along the positive x axis. The world lines of both ends of the metre stick are consequently vertical. Now consider another primed frame moving at velocity v relative to...
  35. S

    B What happens to speed and velocity in a rotating frame of reference?

    Let's say I can see a star in a distance of 1ly in front of me. I'm sitting on an office chair and begin to rotate with a speed of 1/s (1 rotation per second). Then I consider me as not rotating and everything else as rotating. Now I will see the star traveling a circular path with the...
  36. archaic

    Free fall time in an accelerating frame of reference

    This is my wrong attempt, the bolt's equation for ##t\geq 2## would be ##y_b(t)=-\frac{1}{2}g(t-2)^2+e(2)+l## where ##e(t)=\frac{1}{2}wt^2## the position of the elevator's floor in the absolute frame of reference. ##d(t)=-\frac{1}{2}(w+g)t^2+2gt+2(w-g)+l## the distance between the bolt and the...
  37. S

    B Attribution of Reference Frame: A Dilettante's Question

    I can't find an answer on my dilettante question about how we attribute reference frame to complex objects, where different parts move with different velocity or where different parts experience different influence of gravitation. For example, we can take a human's body. If we take the full...
  38. K

    Type of Joints in portal frame

    I was told that for building portal frame, the beam to column connection must be rigid , which means, it has to be fixed , while the column to foundation connection can be either fixed or pinned, am I right ? I couldn't find anything about this online . Pls help
  39. R

    I The velocity of a moving frame of reference

    In the attached fig 1 you have a moving frame of reference (MFR) moving in the direction V at velocity V Looking from above in the MFR there are 2 identical train carriages (car 1 and car 2), Car 1 is on a long set of tracks. Car 2 cannot move but is on train tracks. There are also 2 Identical...
  40. JD_PM

    I Do ##\vec E## and ##\vec B## change in a moving frame?

    I want to understand how electric and magnetic fields change as measured from an inertial frame ##S## vs. as measured from an inertial frame ##\bar {S}## (which has uniform speed v wrt ##S##). I am working out the following example to do so: We have a cylindrical symmetric wire of radius R...
  41. S

    Classical Book about center of mass frame of reference and fictitious force

    Hello I have learned about conservation of momentum, Newton's law (1st, 2nd, 3rd law + free body diagram), conservation of energy and finding center of mass of several 2 D and 3 D shapes (non - calculus method). I watched youtube video about two objects connected by horizontal spring and in...
  42. Geofleur

    I Boosting to an instantaneous rest frame

    The four-velocity and four-acceleration of a particle may be written as ## (V^\mu) = \gamma(\textbf{v},c) ## and ## (A^\mu) = \gamma \left(\frac{d\gamma}{dt}\textbf{v}+\gamma\frac{d\textbf{v}}{dt},c\frac{d\gamma}{dt} \right)##. where ## \gamma ## is the Lorentz factor, ## \textbf{v} ## is...
  43. G

    A Can an object be at rest in its own reference frame?

    In classical physics, every object is obviously at rest with itself, and it makes perfect sense for this to be true. But would this violate the uncertainty principle for a particle? If you are the particle and you know that you're at rest with respect to yourself, you know both your location...
  44. P

    Solving for c: Speed of Q2 in Q1 Reference Frame

    I've tried using this equation: Where: u' = 0.86c v = 0.3c u = Is the speed of Q2 as measured by an observer in the reference frame of Q1 = 0.922c Where have I gone wrong? Have I missed a negative symbol?
  45. M

    B Polarized Electron in a Rotating Reference Frame

    I tried asking a similar question in cosmology but got no answer there so here goes... Suppose I am on a windowless spacecraft in the middle of an intergalactic void. I know that the spacecraft is spinning from measuring the centrifugal forces but have no way of observing the outside...
  46. T

    Restframe of Photon: Explained

    Consider a mass in its restframe relative to which another mass can have an arbitrary velocity ##v < c##. Now consider a photon in its hypothetical restframe. Can a mass have an arbitrary velocity ##v < c## relative to the photon?
  47. Wes Tausend

    Question about "Rest frame of a photon" FAQ

    [Moderator's note: This thread has been separated out from the FAQ entry since questions or suggestions about FAQ entries should not be cluttering up the FAQ entries themselves.] I would like to suggest that it might be more proper to base the "rest frame of a photon" theory explanation...
  48. D

    Angular momentum of a system relative to a moving reference frame.

    I don't have too much of a clue of how to begin the problem. I first wrote the angular moementum of the system of particles: →M=∑mi(→ri×→vi)M→=∑mi(r→i×v→i). Then I know that the angular momentum from of the moving reference frame would have the velocity as the sum of the velocity of the frame...
  49. Kaguro

    What is the Transformation of Four-Velocity between Frames?

    Rod R1 has a rest length `1m and rod R2 has rest length 2m. R1 is moving towards right with velocity v and R2 is moving towards left with velocity v with respect to lab frame. If R2 has length 1m in rest frame of R1, then v/c is what? ----------------------- I let vel of R1 be u, of R2 be w...
  50. Abhishek11235

    Is This the Proper Frame for Your Needs?

    The attempt is above
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