What is Lenght: Definition and 38 Discussions

Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the International System of Units (SI) system the base unit for length is the metre.
Length is commonly understood to mean the most extended dimension of a fixed object. However, this is not always the case and may depend on the position the object is in.
Various terms for the length of a fixed object are used, and these include height, which is vertical length or vertical extent, and width, breadth or depth. Height is used when there is a base from which vertical measurements can be taken. Width or breadth usually refer to a shorter dimension when length is the longest one. Depth is used for the third dimension of a three dimensional object.Length is the measure of one spatial dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed).

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  1. Arman777

    Finding the Wavefunction for Tunneling,with tunnel lenght L

    Homework Statement Let us suppose we have a particle with energy ##E## and ##E<U## and the potential defined as ##U(x)=0## for ##x<0## (I) ##U(x)=U## for ##0<x<L## (II) ##U(x)=U_0## for ##x>L## (III) In this case ##E>U_0## and ##U>U_0## Homework Equations $$HΨ=EΨ$$ The Attempt at a...
  2. Bunny-chan

    Conservation of the string length in pulleys

    Homework Statement This is a common massless string and pulleys problem. I'd just like to understand why, according to the solution, l_2 + 2l_1 = constant. It doesn't seem to me that two times the l_1 length is equivalent to l_2. Can somebody explain? Homework EquationsThe Attempt at a Solution
  3. I

    Special Relativity: Lenght contraction and a photon.

    Reading an old thread (wich is now closed or i would post the question there) there was a discussion about the size of a photon, and if it was an adequate question at all. The discussion on the other thread couldn't agree on a response. Yet there was some postulates that could work with this...
  4. M

    Need to find the length and deflection of bending element

    Hi, I have a task and don't know the good solution. (I add the picture of my task.) I need to find the right length and deflection and to check if the results didn't exceed the allowable stress. I know the value of "q" (force). Also I could choose myself the lenght, but I need to check, if my...
  5. Quarlep

    Is there a definitive measurement in the universe?

    In Every measurement there must be uncertanity.In length or In time everything.Lets assume we have a ruler and a rope.If I measure the rope I get a result but I can't say this is exactly true because there's a unncertanity in measurement.Lets suppoe the rope is 100 cm minus or plus 0.5 mm.The...
  6. vyas22

    Is There a Maximum Distance Limit in Our Universe?

    Hello all, If Planck length (1.61619926 × 10(-35 )meters) places a theoretical limit on minimum possible distance does it also imply that we have a maximum theoretical limit on measurable length as inverse of Planck length (1/Planck Length).. does there any such limit on the maximum...
  7. J

    Radius of circumference as function of arc lenght and height

    Homework Statement I don't know the radius of the circumference. I could only measure the arc lenght, and the height. I know the guidelines say we should not post images, but this is a geometric problem and I think it is something logic to show it with a picture. So the variables are the...
  8. Daaavde

    Pressure gradient in Jeans Lenght

    All the demonstrations on Jeans instability start with: \rho g \ge \nabla P Then they substitute \nabla P with nkT/R. But from ideal gas law: PV = nkT, so P = nkT/V = nkT/R^3 (I'm not interested in proportionality factors, so let's not bother about 4/3 \pi, ecc...) Now, gradient of P, to...
  9. S

    Lenght Contractions in Inertial Reference Frames

    can inertial reference frame ever have "lenght contractions" in 3d or in rest? hi! thank you for all answers in this topic in previous threatin same topic. i open this new thread in same topic but here i try to keep the issue here very short and readable , with no speculation and concentrating...
  10. M

    Simulating earth rotation and (excess) Lenght of Day calculation

    Hello everybody :smile:, I'm new here and hope you can help me with this problem. I have to simulate the Earth rotation with eulers equations of motion (without external torques at first). I have given: Solution of eulers equation without external torques: \omega = (x, y, z)'...
  11. L

    Difference between corelation function and corelation lenght

    For example if we look Ising model correlation function is \langle S_iS_{i+j}\rangle So we can see that if we took into acount just nearest neighbours interraction we also will see that some i+j-th spin feels i-th spin. So there is some correlation between them. Am I right? This is...
  12. L

    Determine the lenght of arc and the area of the sector subtended by an

    Determine the length of arc and the area of the sector subtended by an angle of 60° in circle of radius 3 m Ok First change 60to radian measure. 60 x pi / 180° = 2pi / 6 Then.. I used the formula s = rθ 3(2pi/6) = 6pi/6 = pi <--- Is this right?? And how can I find the area which...
  13. Z

    Variational Calculus - Minimal Arc lenght for given surface

    Homework Statement A curve is enclosing constant area P. By means of variational calculus show, that the curve with minimal arc length is a circle,Homework Equations The Attempt at a Solution F(t)= \int_{x_{1}}^{x_{2}}\sqrt{1+(f^{'})^{2}}dt G(t)= \int_{x_{1}}^{x_{2}}f(t)=const If i use...
  14. A

    About confusion of lenght contraction, and possiblity of length expansion

    hello people... i have a doubt regarding Lorentz length contraction... according to what he described, the length of a body measured in a moving frame appears shorter as compared to the one taken by an observer at rest...if a train moving with uniform relativistic velocity , is thought of...
  15. M

    Displacment and path lenght

    Displacment and path lenght... Is path length the same as displacement?
  16. A

    Length Contraction: Observing Light Hits on a Train

    Regarding the observer riding on the middle of the train sees the light strike first the fwd first and then the aft. Will it be safe to say that for the observer to see the light strikes them both at the same time to adjust the tail of the train by shortening the train so that light can arrive...
  17. M

    Carbonyl Group, C=O bond lenght

    Homework Statement The Questions asks if the C=O bond length is shortened due to resonance Homework Equations The Attempt at a Solution Now, I know that double bonds are stronger than a single bond and the strength outweighs the repulsion by the electrons. I'm just hesitant to say...
  18. C

    Lenght contraction of a charged wire and time dilation?

    In my class we were doing examples with a current carrying wire and if we moved with a speed v we would see length contraction. And because of this the moving line charge would go up in value and we would see an Electric field. And then we did the same for a solenoid but he said we need to...
  19. W

    Calculate Lens Focal Length - Convex & Concave Lenses

    Homework Statement I have an actually interesting practical homework. I need to calculate the optical strength (hope I translated it right, D=1/F), to do I need to find the lens focal length. I need to find my self a concave and a convex lens. I don't have a concave lens (I think), but I do...
  20. P

    Calc3 vectors, lenght of curve, equation of the sphere.

    1.Consider the process A[1,1] and B [-1,4]; let Vector U=AB 1a.Write u using components. Write u using the standard basis. 1b.Draw u as a position vector. Find u. 1c.If C [1,1] and D [5,y], then find the value of y so that AB is parallel to CD. 2. Find the length of the curve 2t2 3t2 ...
  21. D

    Focal Length of Lens: Object 5 cm Tall, 10 cm Away

    An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal length of the lens? I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to...
  22. D

    What is the lenght of the lever arm? (when torque and force are given)

    Homework Statement If a torque of 55N.m is required and the largest force that can be exerted by you is 135N, what is the length of the lever arm that must be used? Homework Equations Lever Arm=(r)(sin) Torque=(Force)(r)(sin) The Attempt at a Solution To be honest, I'm stumped
  23. R

    DSP: What do you mean by the Filter Lenght?

    What does the length of the filter in DSP means? What does it refer physical or practical when it states that "signal transmission path models have long impulse response?" And why do audio signal transmission paths have long impulse response?
  24. P

    Graphing conves lense relationships to find focal lenght with slope

    Homework Statement I need to find the relationship between object-lens distance and image-lens distance for a lense(converging) but cannot graph the relationship in a way that the focal length is the slope for the graph Homework Equations 1/u + 1/v = 1/f where u= object lense distance...
  25. C

    Calculating the lenght of a year on mars?

    Homework Statement The mean radius for the orbit of the planet Mars about the sun is 2.28 * 1011m. If the radius of the orbit of the Earth around the sun is 1.49 * 1011m. If it takes the Earth 1 year (365 days) to orbit the sun, how long (in Earth days) is the year on mars? So this is the...
  26. R

    Calculating wire lenght for an air core inductor

    I would like to build an air coil that will create a flux field, which will in turn induce a closed loop coil, that results in an equal and opposite force. The power source is an array of PV cells hooked up in series or parallel which ever will give the air coil the greatest/strongest magnetic...
  27. 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...
  28. R

    How long does it take for wave to travel the lenght of the string

    Homework Statement Fundamental frequency of a string fixed at both ends is 256 Hz. How long does it take for a wave to travel the length of string? Homework Equations V = f (lambda) Otherwise, not really sure. The Attempt at a Solution I didn't really know how to approach...
  29. C

    How Do You Calculate Wavelength of Infrared Radiation in Micrometers?

    Homework Statement Calculate the wavelength in micrometer of infrared radiation whose frequency is 3.10 × 10^14 Hz. Express answer in scientific notation. speed of light = 3.00 x 10^8 m/s Homework Equations wave length = speed of light/frequency The Attempt at a Solution 1...
  30. A

    De Broglie Wave Lenght And Number Of Waves K

    I could not understand very well because of the argument between me and the teacher about k space and wave length of de broglie because he said that we can not explain solid state or lattice or crystal only by suing k space or vector k not by using de broglie wave length because de broglie wave...
  31. P

    Lenght to volume conversions

    Hey guys, I have a question. I understand conversion units but how does one convert from Length to volume. Example. convert 12.7m to cubic inches? If I am thinking correctly you convert m to m^3 by cubing 12.7 which becomes 2048.4m^3. Is that right? I then find to conversion factor for m to...
  32. L

    Calculating Wire Gauge for Length & Amp Rating

    Need help. Is there a simple formula to calculate the gauge of wire to use vs. length for a know amp rating of a device. I have a device I need to install a couple of hundred feet from the house and know the amps it pulls but do not know the formula to figure the best gauge wire to run to it...
  33. M

    Length Vector Rotation Matrix Constraints | Preserve A

    what constraints must the elements of three dimensional rotation matrix satisfy in order to preserve length of vector A
  34. M

    Finding the Length of a Curve: Step-by-Step Guide

    i got a problem that says: x=sqrt(5)sin2t -2 y=sqrt(5)cos2t - sqrt(3) how would i go about starting it?
  35. quasar987

    Length of Line between 2 Points on Circle

    Hi, I'd like to know the name for the length in a circle that I will describe: Consider 2 arbitrary points lying on the perimeter of a circle. I'm talking about the shortest distance distance between these those points. (i.e. the straight line joining them.) Thx
  36. E

    A Graph with Closed Paths of Even Lenght is Bipartite?

    The title says it all. I'm having trouble showing: If G is a graphs where all the closed paths in G are of even length, then G is bipartite. G is bipartite if I can find 2 vertex sets V and U such that every edge is of the form (v,u), v in V and u in U. I was thinking of the following...
  37. P

    Lenght contraction experiments.

    My question is rather simple: Are there experiments where they have measured length contractions?
  38. D

    Is the Concept of Zero Length Contraction Possible in Special Relativity?

    In Einstein's SR the velocity of the light (c) is same in every referent frame. Let us for instance assume we don't know its exact value and try to estimate it. The relative distance suffers contractions depending on the velocity of the frame like this: L=L_0\sqrt{1-\frac{V^2}{c^2}} where L0...