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. S

    Length Contraction (Dilation?)

    Do fast moving objects in relative motion always observe length contraction regardless of their direction of travel? In every example I find the train or the rod appears to be “moving toward you.” I can’t find any thought experiments describing what happens after you pass the train and it...
  2. Fredrik

    The terms length contraction and time dilation

    The terms "length contraction" and "time dilation" Is there a particular reason why we say length contraction but time dilation? A Lorentz transformation \Lambda=\gamma\begin{pmatrix}1 & -v\\ -v & 1\end{pmatrix} takes \begin{pmatrix}1\\ 0\end{pmatrix} to \gamma\begin{pmatrix}1\\...
  3. D

    Length contraction and the direction of motion

    Can length contraction be treated as a vector? E.g. Suppose I am traveling 10 degrees north of east. Will my length contraction with respect to the east direction be cos 10 times the appropriate Lorentz transformation (with respect to the direction of motion)? Thanks.
  4. D.S.Beyer

    Gravitational Length Contraction and Dilation?

    My interest surrounds the qualities and affects of gravitational length contraction (GLC). Like most other General Relativity circumstances GLC is difficult to measure because of frame of reference issues (such that a meter in space is longer than a meter on Earth but in both frames of...
  5. T

    Length contraction or Lorentz Contraction

    As I understand it, Lorentz Contraction states an object "contracts" relative to it's velocity to an observer. So at a high velocity of speed, the meter stick (carried by the object moving relative to the observer) appears to contract (to the observer) and the observer measures less distance...
  6. T

    Length contraction and time dilation equivelant?

    Hi, i asked this before but i think i found a clearer way to define my quesiton. As i asked in the title, does length contradicts as a result of time dilation? Or time dilation and length contraction are equal? When we deal with formulas generally we use the vertical clock and derive time...
  7. P

    Speed of light is 40mph. Time Dilation and Length Contraction

    Homework Statement Suppose that the speed of light in a vacuum ( c), instead of being a whooping 3x108, was a rather sluggish 40.0 mph. How would that affect everyday life? Throughout this problem we are going to assume that c = 40.0 mph and that time dilation is in full effect. Let's start...
  8. R

    Twin paradox and length contraction

    We know that the twin paradox is not a paradox since one of the twins accelerate and time passes more slowly for him relative to his twin on earth. My question is why can't we apply the same reasoning for length contraction? If one of the twin A measures the lengths of sticks in the reference...
  9. T

    Length contraction (objects & space or objects only)

    Does length contraction apply only to objects, or to space as well? On the one hand, sources like this seem to imply that it applies only to objects: http://en.wikipedia.org/wiki/Bell%27s_spaceship_paradox On the other hand, most people on this forum seem to believe it applies to space as...
  10. T

    Confused about time dilain length contraction

    hi, we all know when we derive the time dialtion formula we choose a vertical light clock, and basically since the light take a longer zig-zag path to the stationary observer, the time is dilated. That's ok but when deriving length contraction, firstly we accept time dilation for horizontal...
  11. jaketodd

    Length Contraction: Does Size Change Affect Density or Radiated Energy?

    Length contraction is one of the main aspects of relativity. However, I have a question: When something undergoes length contraction, does it become more dense or, is the decrease in length radiated in some way? Thank you, Jake
  12. H

    Gravity and Time Dilation: Length Contraction and Mass Inflation?

    According to SR theory, relative motion leads to -length contraction -mass inflation -time dilation. In GR theory, gravity leads to time dilation. Does it also lead to -length contraction? -mass inflation?
  13. B

    Length contraction, hubble constant, and C

    Question: As an object approaches C and its length contracts, does space-time contract also, causing the a larger range of the universe to become visible? I.e. if the Hubble space telescope was traveling at high velocity, would it gain access to light from more distant galaxies than it has...
  14. H

    Length Contraction spaceship Problem

    Homework Statement A spaceship passes you at a speed of .750c. You measure its length to be 28.2 m. How long would it be when at rest? Homework Equations I think the equation that is relevant is L=L(sub0)xsqrt(1-v^2/c^2) The Attempt at a Solution L=28.2xsqrt(1-(.75^2))=18.65m...
  15. E

    Twin paradox without length contraction

    Hi all, apologies if this has been posted a million times before... I'm trying to explain the twin paradox without getting involved with length contraction. One way to think of it is Twin A remains at rest on Earth then twin B goes off at 4c/5 to Alpha centauri 4 light years away, then...
  16. R

    How Does Length Contraction Affect Measurements in Different Reference Frames?

    Homework Statement A meter stick at rest in S' is tilted at an angle of 30 degrees to the x'axis. If S' moves a speed beta = 0.8 with respect to S. a)How long is the the meter stick as measured in S ? b)What angle does it make with the x-axis? Homework Equations l=l naught/gamma The...
  17. N

    Length Contraction Documentary

    I need help with length contraction. I need videos that explains or proves that length contraction is possible even if it is just the visual interpretation of an observer. pls help.
  18. R

    Length contraction and interstellar travel

    Interstellar travel is always a problem in science fiction: you can't have the hero hibernate for millions of years whenever he or she wants to travel to another star, but it's annoying when spaceships just magically move faster than light. However, wouldn't length contraction from special...
  19. W

    How Does Length Contraction Affect Measurements in Special Relativity?

    Homework Statement A spaceship travels past a planet at a speed of 0.80 c as measured from the planets frame of reference. An observer on the planet measures the length of a moving spaceship to be 40m. a)How long is the spaceship, according to the astronaut? b) At what speed would the...
  20. D

    Special Relativity - Length Contraction Problem

    Homework Statement The radius of our galaxy is 3x10^20m (30000 lightyears). (part a): Can a person in principle travel from the center to the edge of the galaxy in a normal lifetime? Explain using Time-Dilation, then Length-Contraction. Homework Equations d\tau = dt \sqrt{1...
  21. T

    Length contraction falling down a hole.

    Ok, so imagine observer A is moving along with a measuring rod of length L that is being slid along the ground by a rod that holds it steady by pushing it against the ground as it slides (no tilting whatsoever, the base of the rod remains firm against the ground), at a velocity comparable to c...
  22. M

    Length contraction in a current carrying wire?

    Reading http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Length_Contraction I reminded something that always bothered me about this explanation: I would think that a current carrying wire would only appear electrically neutral when the observer is moving along the wire...
  23. E

    Is there any derivation of length contraction through proper lenght?

    I'm doing some sort of notes on special relativity and i got this question, because proper time and time dilation have a relation. In fact we have that proper time is mathematically the arc length of a timelike curve. I will use geometrical units and the Minkowski Metric with the -+++ signature...
  24. maverick280857

    Length Contraction Question from Rindler

    Hi, this isn't exactly homework, as I'm teaching myself, but I thought this forum would be more appropriate for it. Homework Statement (Page 36, Introduction to Special Relativity by Wolfgang Rindler) An 18-foot pole, while remaining parallel to the x-axis, moves with velocity (v,-w,0)...
  25. Rasalhague

    Length contraction: a question about tramwheels

    This isn’t an example from a textbook, just something that occurred to me, so there may be any number of mistaken assumptions in it. I must have gone wrong somewhere, but I don't know where, and I'd appreciate any advice. Imagine one of those Swiss high speed trams that wreaked so much havoc...
  26. A

    Why Does Length Contraction Happen?

    Ok, I do understand what it is, that things get shorter the faster you go.. But I just want to know why they do?? If anyone could explain to me... Someone told me it was just an illusion because our eyes couldn't keep up but I think that person was wrong, so thank you to anyone that can help :)
  27. P

    The Correct Time on the Clock During the Presentation Ceremony?

    Homework Statement 1)An ex-student with a new spacecraft 'buzzes' the school oval on sports day at 1.5 * 10^8 m/s. How long does the 100m track appear to him. 2) The sports day began at 9am. The student buzzed the school at an average speed of 0.5c till the presentation ceremony at...
  28. S

    Help with length contraction and relativistic momentum please

    Homework Statement A woman is 2.0 m tall and has a mass of 60 kg. She moves past an observer with the direction of the motion parallel to her height. The observer measures her relativistic momentum to have a magnitude of 2.30x1010 kg·m/s. What does the observer measure for her height?Homework...
  29. C

    Length Contraction and a Relativistic Angle

    Homework Statement A ladder 4.92 m long leans against a wall inside a spaceship. From the point of view of a person on the ship, the base of the ladder is 3.13 m from the wall, and the top of the ladder is 4.00 m above the floor. The spaceship moves past the Earth with a speed of 0.919c in a...
  30. F

    Special Relativity: Why is Length Contraction Inverse of Time Dilation?

    Homework Statement Hello I actually just need help with an explanation rather than equations (I hope this is OK). In my essay I need to explain why the length contraction in Special Relativity is the inverse of the time dilation factor. My explanation is below, but I'm not convinced...
  31. B

    Clarification on length contraction

    I ask this just to clarify something, because something I read threw me off earlier. An object travels near the speed of light, and you are stationary. You measure the object somehow, and find it's length from your reference frame. Would it's length be shorter or longer than the proper...
  32. F

    Length Contraction: Light & Spaceships

    I understand the explanation for time dilation involving the light clock on the spaceship, or a train. But what is used to explain length contraction. Is there another example that is used involving a light beam and a spaceship.
  33. F

    Is Length Contraction Real or Just an Illusion at High Speeds?

    In SR is length contraction physically real, or is it just and illusion brought on by high speed motion.
  34. N

    Benefits of time dilation / length contraction pairing?

    There have been more than a few threads where there clearly is confusion about the use of time dilation and length contraction. People initially think that: 1. in an frame which is in motion relative to themselves, time dilates and lengths contract; and 2. velocities in a frame which is...
  35. Mentallic

    Length Contraction in Particle Accelerators

    So does there exist any evidence to support the theory of length contraction? I am aware of the overwhelming evidence to support time and mass dilation, but none for length.
  36. S

    So, thank you very much again.Why not length contraction?

    Hi everybody, I have a question concerning length contraction/time dilation. I read about how time dilation is calculated using transverse motion and how length contraction is calculated using longtitudinal motion in order to preserve lightspeed and it got me thinking: why not use length...
  37. Z

    Length contraction in Lorentzian relativity

    Hi, I'm trying to understand Lorentzian relativity (Lorentz ether theory, whatever) which is empirically equivalent to the Einsteinian STR. I have, however, a problem in comprehending length contraction. In the Lorentz theory we have a preferred frame and length contraction is a real...
  38. Chewy0087

    Derivation of Length Contraction (special relativity)

    Homework Statement Show the derivation for legnth contraction, given that from the example given; The example shows a moving light clock - two walls which are moving in a direction at speed u and a beam of light from wall A to wall B then back to A and so forth. From Ao (starting...
  39. P

    Length contraction and magnetic field

    Some days ago there was a discussion on pf whether eath’s magnetic field was rotating. That got me to think again about magnetism and relativity and I found this article: http://en.wikibooks.org/wiki/Special_Relativity/Simultaneity,_time_dilation_and_length_contraction Including this section...
  40. S

    Length Contraction from an Angle

    Homework Statement A meter stick is moving with 0.8C relative to frame S. What is the sticks length when measured by an observer in S if the stick is 60 degrees to v, as seen in the rest frame? Homework Equations Length contraction = proper length /lorentz factor The Attempt at a...
  41. Q

    Percent Length Contraction (check solution)

    Question: What is the percent length contraction of an aircraft traveling at Mach 2? So, we know that Mach 2= 680.58 m/s and that L'=L\sqrt{1-(v/c)^2} If you divide over the L to get: L'/L=\sqrt{1-(v/c)^2}=% length contraction Plug-n-chug from here to get...
  42. C

    Gravity and Length Contraction

    I was wondering whether or not the Earth would have a larger gravitational force, relative to me, if I passed the Earth at close to the speed of light? The reason I ask is if I pass the Earth by then it appears to be flatened, but only in the direction of its motion. So, if its length...
  43. F

    Is relativistic effect of length contraction physically unreal ?

    Is relativistic effect of length contraction physically "unreal"? One guru indicate that Length contraction has nothing to do with compression. It is more correct to view length contraction as a rotation in space time. If we rotate a box filled with gas or perfect fluid, clearly its density...
  44. A

    Length Contraction: What Does it Mean for Mass?

    Homework Statement A spear moves past you at a very high speed. As it passes, you measure its length at one half its normal length. From this measurement, what can you conclude about the moving spear's mass? Homework Equations The Attempt at a Solution To have the spear appear...
  45. D

    Time dilation and length contraction help

    The average lifetime of a muon is 2.2 microsec. What is the average distance the muon would travel in free space before decaying according to a stationary observer watching the muon travel with a speed of (.60c). I know how to find the proper time. 2.2/Sqrt[1-(.6c/c)^2] = 2.2/Sqrt[1-.6^2]...
  46. A

    Length Contraction Homework: Find Length of Moving Rod

    Homework Statement A rod of rest length L0 = 10.4 m moves with a speed v = 0.42c along the x axis. The rod makes an angle of q0 = 66.1° with respect to the x' axis (primed frame is moving with the rod). What is the length of the rod as measured by a stationary observer? Homework Equations...
  47. M

    Derivation of Time Dilation and Length Contraction from Lorentz Transformation

    Hello there, a simple special relativity question, how can the Time Dilation and Length Contraction Formulas be derived from the Lorentz Transformation Equations?
  48. Y

    Question about length contraction

    In most special relativity primer book, length contraction section, the length is always defined or measured by the time of a light flashing at one end of a rod, traveling to the other end, reaching a mirror and reflecting back to the first end. Please read this example if I did not make...
  49. J

    The Nature of length contraction

    Can someone please clear up the nature of length contraction Does the spatial dimension parallel to the motion of a moving metre stick contract (as seen by a stationary observer). Or Is contraction a purelly matter phenomenon whereby space is constant and the actual material of the...
  50. S

    Length contraction depends on the distance of the object?

    http://home.orange.nl/kuip3148/phys1.JPG Not exactly homework, but a problem I found in my lecture notes. The train is moving at a constant speed 0.5c. Question b asks what the length of the train will be then at t = -1. From what I understand, this suggests that length contraction depends...
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