What is Length contraction: Definition and 475 Discussions

Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length, which is the length as measured in the object's own rest frame. It is also known as Lorentz contraction or Lorentz–FitzGerald contraction (after Hendrik Lorentz and George Francis FitzGerald) and is usually only noticeable at a substantial fraction of the speed of light. Length contraction is only in the direction in which the body is travelling. For standard objects, this effect is negligible at everyday speeds, and can be ignored for all regular purposes, only becoming significant as the object approaches the speed of light relative to the observer.

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  1. P

    Special Relativity: Time Dilation and Length Contraction

    Hi, I have attempted the following questions but I am unsure of my answers/method. Could you guys please help me through? A super fast spacecraft is moving at a speed of 0.80c with respect to the observers on Earth. The spacecraft leaves Earth in May 2004 on its way to a distant solar...
  2. P

    Is length contraction direction independent?

    U is the universal rest frame. A and B space ships pass U at t=0, moving at v. Both experience equal length contraction in the x direction. If length contraction is a result of em deformation in response to acceleration, then length expansion should be the response to deceleration. If the B...
  3. bcrowell

    Justification of length contraction in light-clock presentation

    Suppose you've just established the existence of time dilation using Einstein's 1905 postulates and the light clock. Is there any nice, easy way to go on and prove length contraction? Here are a couple of incorrect arguments that I've been guilty of using in the past: Symmetry: The Lorentz...
  4. P

    Why does length contraction only occur parallel to the direction of motion?

    why does space time not contract uniformly in every direction around a fast moving object?
  5. T

    Length Contraction of observers approaching an object

    Homework Statement Two momentarily coincident observers approach a small and distant object. One measures the object to be twice as large as the other's measurement. Find their relative velocity. Homework Equations Lorentz Transforms L/L_0 = \sqrt(1 - \beta^2) The Attempt at...
  6. S

    Solve Length Contraction Homework: Find v

    Homework Statement A spaceship moves past you at speed v. You measure the ship to be 300 m long, whereas an astronaut on the ship measures a length of 356 m. Find v. Homework Equations L=L1sqrt(1-v^2/c^2) The Attempt at a Solution I have tried this by using the above formula. I...
  7. A

    Length contraction in an inelastic collision

    Preparing for a classical prelim by going over previous exams. Homework Statement A relativistic meter stick moves with speed v in the lab. It collides head on with an impenetrable wall completely inelastically, thereby coming to rest in the lab frame. What is the maximum length of the stick...
  8. grav-universe

    GR Length Contraction & Shapiro Delay: Investigating Light Speed

    In this thread in another forum, I calculated the coordinate speed of light as measured by a distant observer. As far as I understand it, the length contraction in GR is only in the radial direction, right? None tangent, correct? The time delay of light found, though, trying different examples...
  9. coktail

    Relativity of length contraction

    If two clocks with observers attach to them move away from each with symmetrical acceleration, they will experience symmetrical time dilation, meaning they both see the rate of each other's clocks slow down relative to their own. However, if the acceleration is asymmetrical, the time dilation...
  10. J

    Length contraction of falling things

    1: Does an observer, standing on the moon, see a brick, that is falling straight down, to contract? 2: Does an observer, standing on the moon, see a light pulse, that is falling straight down, to contract?
  11. S

    How to get time dilation & length contraction from Lorentz transform?

    OK, I've found a great explanation of the derivation of the Lorentz transformation, with x' = γ [ x - v t ] t' = γ [ t - ( v / c2 ) x ] so if I take the other term as 0, there is x'( t = 0 ) = γ x t'( x = 0 ) = γ t but the problem is that the time dilation & length...
  12. harts

    Spaceship question: Problems with Length Contraction

    Homework Statement Two spaceships having rest length 100 m pass each other traveling opposite directions with a relative speed of 0.901 c As the front of the spaceships just cross, each pilot sets off a small flare at the back of her own ship, synchronized to the same instant (t=0 in her own...
  13. P

    On length contraction (Special Relativity)

    Homework Statement Show that the length contraction deforms a sphere in motion to an oblate rotational ellipsoid whose volume decreases by a factor of γ (gamma) Homework Equations x=x'/γ v=4∏r^3/3 (volume for sphere) v=4∏(a^2)b/3 (volume for prolate and oblate spheroid) The...
  14. G

    Misunderstanding time dilation and length contraction

    hi sorry about my english. i am from france. i have a few questions about the image i have found in my schoolbook that i attached to this post. there is a light signal moving up and down and each time it reaches the upper mirror this is somehow detected. there are also two observers: one...
  15. johann1301

    Length contraction and general relativity

    Can one detect length contraction due to general relativity? I.e does length/width/height change with distance to a gravitational centre? If so does the object get longer or shorter? I know this is the case with increasing speed in special relativity, but what about GR... If i went into...
  16. D

    Length Contraction - altitude?

    An observer on Earth sees a meteor approaching rapidly, heading directly for the Earth's surface. At a certain instant, the Earth observer sees the meteor at 650m altitude. If the meteor is traveling at 0.92c, as recorded by an Earth radar, what would be the altitude as measured by the alien...
  17. J

    Why Time and Length Contraction/ Expansion

    I have been wondering why the universe should behave in such a way. There is no obvious reason why gravity or speed should change the rate you travel through time or the relative distances, 1 second should be 1 second and 1 metre 1 metre whatever the strength of gravity or speed. The only...
  18. V

    Length Contraction and Relative Motion

    Consider two observers in relative motion.At x'=0, t'=0, x=0, t=0. There's a box at distance x metres in the unprimed frame. Since the primed frame moves with a relative velocity v, he observes the length x to be contracted by a factor gamma. Does this imply that when the obsever in the unprimed...
  19. C

    Question about length contraction.

    Lets say I have 2 charged spheres that are connected by a spring and they are a distance d apart. The spring is made of a material that will not allow the charge to evenly distribute. And each sphere has the same charge q on it. Now I move with respect to this object and I should see the spring...
  20. B

    Clarification about length contraction question

    A space traveler is very happy to discover that after a long period of 1 g acceleration the measured distance to his destination has contracted substantially. At some point he begins to plan for reversing thrust... It come to him that if he reduces the relative speed between his craft and...
  21. K

    Length contraction - problems with transformation and time

    Homework Statement Hello, I have a question about length contraction transformation. In my textbook it looks like this: x_1=γ(x_1'+ut'), x_2=γ(x_2'+ut') If the coordinates of the two events are (x_1,t_1), (x_2, t_2) , why is t used instead of t_1and t_2? The second problem I have is with...
  22. M

    Was gravitational length contraction predicted by general theory of relativity ?

    I have read somewhere about the phenomenon called gravitational length contraction.Was gravitational length contraction predicted by general theory of relativity?
  23. E

    Special Relativity length contraction and velocity

    Homework Statement Λ particle has a proper life-time τ = 2×10−10 s. After being born in the cloud chamber (a device to track energetic particles) of physics laboratory it left there a a 300cm long trail. Find the speed of this particle in the laboratory frame. Homework Equations...
  24. M

    Calculating Muon Half-Life: Length Contraction vs Time Dilation

    This link is confusing me. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html In this link, with non-relativistic method, half life is calculated as 21.8. But with relativistic method half life is calculated as 4.36. We calculate half life considering time dilation for muon...
  25. S

    Closing speed and length contraction paradoxes

    A google search revealed an often asked question (including a locked thread here) about two ships approaching with closing speed > c, say each going .75c. And there's always multiple answers from the experts about relative frames and Lorentz this and that and you have to use the special formula...
  26. S

    Applying time dilation and length contraction to measure parralel c

    The title isn't quite clear, because the question was a little too long. Here it is in full: How to apply length contraction and time dilation to a moving observer to measure the speed of light of a light beam moving parallel to their reference frame. Imagery and familiarity are my...
  27. M

    Length Contraction rearrangement

    Hello, Suppose, There is two points [t_{a1}, x_{a1}] and [t_{a2}, x_{a2}] stationary in my frame A. I say L_a=x_{a2}-x_{a1}. If I want to find x component of co-ordinates in other frame B which is moving relative to me with constant speed v. I have to use the equation 1...
  28. A

    Potential Energy of Length Contraction

    Is there any potential energy associated with length contraction? If I start with a rod at rest, and accelerate it to a relavsitic kinetic energy, the rod also length contracts, at least as viewed from the ground frame watching the rod go by. When the rod decelerates and comes to rest, it will...
  29. I

    Time dilation from length contraction

    Suppose there exists an absolute frame. The observer is at rest. an object moves with velocity v. Suppose it contracts as expected. Does this imply automatically that time dilation occurred?
  30. D

    Precise instrument (w,h,l) after length contraction still working?

    To understand length contraction better, would an precise instrument where width, height and length must be exact equal for working when standing still in frame A, still working in its rest frame B at a higher speed in frame A with length contraction ? With other words, is length contraction...
  31. C

    Length contraction near the speed of light

    It is my understanding that an astronaut could get from Earth to the far edge of the Milky Way within the length of a human lifetime if she were traveling close enough to the speed of light. From earth’s perspective, time would pass very slowly for her as she moved across the galaxy. From the...
  32. R

    Length Contraction and Time Dilation in Relativity: An Electron's Perspective

    Homework Statement An electron travels in an accelerator tube at a speed of 0.997 c relative to the Earth. In the frame of the electron, the length of the tube is 1.20 m. A. What is the length of the tube relative to Earth? B. Relative to Earth, how long does it take for the electron to...
  33. D

    Explaining time dilation from length contraction easier

    For the explanation of the Lorentz derivation in Wiki with the known triangle, 2 rest frames are considered in 1 view, so that's not forbidden. So I do too. To explain time dilation is easier to understand if you see it by length contraction. That could be explained somehow in the future...
  34. M

    Modern Physics view of Length Contraction?

    I've been told several times that length contraction is not "real" in the sense of material or its space actually contracting. How does modern physics (by that I mean what is being taught currently) view Bell's spaceship paradox. Will the string break? Why, if length contraction is not real...
  35. R

    Direct observation of lorentz length contraction

    There is a train(think of having only two boggie for a claer visualization ) in which two rod which are attached to the front and rear end of the train(say, the length between these rod is the length of the train). These are lowered by a single lever to touch the ground. These rods are at...
  36. H

    Length Contraction: Solving for L

    Homework Statement A rod of length L_0 moves with a speed v along the horizontal direction. The rod makes an angle of θ_0 with respect to the x'-axis. a. Show that the length of the rod as measured by a stationary observer is given by L = L_o [1 - (v^2 / c^2) cos^2 (θ_o) ]^(.5)...
  37. S

    Relativity: Time Dilation and Length Contraction

    Homework Statement Two events are observed by inertial observer Stampy to occur a spatial distance of 15 c·s apart with the spatial coordinate of the second larger than the spatial coordinate of the first. Stampy also determines that the second event occurred 17 s after the first. According...
  38. K

    Time dilation and Length contraction in Saddle Geometries

    The way I've been reading it, elliptic geometries are due to a positive Gaussian curvature, while hyperbolic geometries are due to a negative Gaussian curvature. Do local saddle curvatures mean local time dilation and length contraction, or do they mean local time acceleration and length...
  39. jbrussell93

    Length contraction on quantum scale?

    How can relativistic length contraction be measured at the quantum scale? Since a Planck length by definition cannot be divided, how can something that is 1 Planck length, traveling near the speed of light, contract with respect to an observer? In other words, how can an observer possibly...
  40. Z

    Lorentz Length Contraction Derivation

    In this video: Special Relativity: Length contraction in more detail http://www.youtube.com/watch?v=s3ZqBt8KWVQ&feature=mfu_in_order&list=UL for the derivation of Lorentz contraction equation at 2.48 the guy says, "I won't bore you with the details". I'd appreciate is someone would...
  41. G

    Time Dilation and Length Contraction the same thing?

    Are these really just two ways of explaining the same thing?
  42. D

    Why are the effects of Time Dilation permanent but Length Contraction is Not?

    This question is in regard to special relativity. From my rudimentary understanding, concerning the twin paradox, if one twin leaves traveling near the speed of light and returns, he will find himself younger than his twin who stayed behind. Hence, the effect of time dilation is permanent...
  43. M

    Does length contraction occur in gravitational fields

    1 does length contraction occur in gravitational fields 2 what is the equation of gravitational length contraction 3 what are the units of measuring mass not weight
  44. Y

    Length contraction and accelerating frames

    We all know the definition of a rope between two identical accelerating spaceships and how that rope will break assuming they both accelerate with the identical same velocity (as defined from a observer on Earth for example). And it makes sense, thinking of stress. But how do I define a Lorentz...
  45. N

    Length Contraction and special relativity

    Homework Statement The dimensions of your friend’s spaceship are 100 meters in length, with a cabin width of 20 meters (i.e., you could approximate the main body of the ship as a cylinder with length 100 meters and diameter 20 meters). However, since your friend’s spaceship is speeding past...
  46. W

    Length contraction problem in special relativity

    Homework Statement A rod of proper length L0 oriented parallel to the x-axis moves with speed u along the x-axis in S. What is the length measured by an observer in S'? Homework Equations Relativistic relative velocity: For an object moving with speed u in S, its speed u' in S' = (u - v)/(1...
  47. C

    Time Dilation and Length Contraction near the Event Horizon of a BH

    A clock falling towards the event horizon of a black hole would appear slowed down to the point of being frozen in time (or almost). But I'd like to understand properly what happens to the length contraction experienced by an observer falling together with that clock. Would he experience...
  48. S

    Can you measure the proper length of a rope when dangling it into a black hole?

    I'll try to be as specific as possible with my question. From my reading of SR I understand that an object that is moving relative to me will be contracted in the direction of its motion. I have no issue with that and I accept it as a fact. Would I be right in thinking that there is also length...
  49. C

    Exploring Quantum Mechanics and Length Contraction

    What if I had a double slit setup and I was shooting electrons through them. But in the rest frame the slits were to big to bring out the diffraction effect. But then suppose I move by the 2 slits at significant speed to length contract the slits to where diffraction would be eminent. Would...
  50. N

    Why does length contraction happen only in the direction of motion?

    Length contraction happens only in direction of motion. Never perpendicular to the motion. My questions are 1) Why is it so?. For an observer in the same frame, it would mean a meter scale to give 2 different results. If by some means he is able to calculate the difference won't he be able to...
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