Questions tagged [length]
The length tag has no usage guidance.
74 questions
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Do solids also follow the reverse of this equation? [closed]
We all know the equation for linear thermal expansion on heating the solid
$$\Delta L = \alpha L \Delta T $$
Now I know solids expand on heating, for example in railway tracks in summers but after ...
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Why does the line element expression contain only second order differential terms? [duplicate]
The general expression of the line element $ds^2$ is $$ds^2 = g_{ij}dX^{i}dX^{j},$$ where $g_{ij}$ is an element of the metric tensor.
Is there a rigorous proof of why there are no terms in the ...
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Are comoving distances time-independent?
A comoving reference frame expands along with the universe, factoring out the effect of the Hubble expansion. Suppose a galaxy has a redshift $z = 1$ and its comoving distance DM is $11 \,\mathrm{Gly} ...
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Is displacement vector always the shortest path?
I read that the displacement vector of a particle is the shortest path between its initial and final positions since it's a straight line joining the two points, this holds true for me till a 2D ...
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The length of four-force
Recently, I'm reading the FeynmanLecture II_26 https://www.feynmanlectures.caltech.edu/II_26.html
It says that the “length” of the four-vector is an invariant under what is called the “complete ...
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Is the meter relative to time?
Is the meter relative when we are near the speed of light?
I was reading a physics book and I found that the meter is the length that light travels for an amount of time, so since time is relative ...
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Has there been a big change in 1983 when the definition of the metre changed?
The metre was defined at the end of the $18^{th}$ century as the ten-millionth part of the quarter of the meridian (from the north pole to equator). Then, from $1983$ the definition changed for the ...
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In real life, we can have a pencil of length 2 cm. Can we have pencil of length $\sqrt{2}$ cm? [duplicate]
In real life, we can have a pencil of length 2 cm. Can we have pencil of length $\sqrt{2}$ cm?
My answer to that was no , we cannot even make 2 cm pencil.
My argument was that when are working ...
user157835
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If the electron has no spatial dimensions based on QM, does not it violate the Planck length as the minimum admissible length for physical entities?
I think the question is self-explanatory: Quantum mechanics insists that electrons have no dimensions as point-like entities, while there is a minimum (non-zero) boundary for length called the Planck ...
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Does a rubber band stretch evenly?
Suppose you have a rubber band, and a point is marked on the rubber band at the 1/3 point. If you now apply force to the two ends of the rubber band to stretch it, will the point maintain its 1/3 ...
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Translating plasma units into SI units
I am trying to compute the characteristic lengths and frequencies in a plasma, namely the electron plasma frequency and electron inertial length. From the NRL plasma formulary
$$\omega_{pe}\ [rad/s] = ...
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3
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Can it be accurate to say that time is also a length?
So a type of measurement, in units, is length, position, mass, etc, and a unit is meters, kilograms, etc.
Is it accurate to say that "an hour" is a time measurement, but also a form of ...
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Parsec confusion
parsec is defined as the distance at which average radius of earth's orbit around sun would subtend an angle of 1''(second of arc). But suppose im looking at this star when earth is on one side of the ...
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What are light years? like you know how people measure some things in light years? what is light years [closed]
so basically you know how scientists measure how far things are but in space and they measure in light years well what are light years and how long are light years?
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How does the length of a double open-ended tube affect its frequency? [closed]
I am attempting to build a trumpet, and need to calculate the lengths of the piping for it. I have attempted to find information on this online, but have been unable to find something that can help me ...
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How accurately do we know how long a meter is?
A meter is, by definition, a specific fraction (1/299792458) of the distance light travels in a vacuum in one second. How accurately do we know how long this is? In principle, it's exactly defined, ...
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What reason/evidence do we have to think that the Planck length is the smallest length possible? [duplicate]
From what I've gathered, Planck length is the smallest measurable length, though we do not know whether it is the smallest length physically possible. The Planck temperature is called the ...
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Does the arc length constant of the sine function interval occur anywhere in physics?
π occurs in many formulae, but does the arc length of a single sine function interval have any meaning in physics? Does it occur in any formula?
According to What is the length of a sine wave from 0 ...
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Is a meter constantly getting bigger? [duplicate]
If the bigbang is the start of the expansion of space everywhere then does that mean that a 1 meter ruler is bigger tomorrow than it was today?
Does this apply to the size of atomic particles and ...
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What is the proportional relation between effective length $L$ and gravitational acceleration $g$ for a simple pendulum? [closed]
The formula of time period of a simple pendulum stands for, $T =2π \sqrt{L/g}$.
● If 2π and $g$ remain constant, $T$ would be proportional to the square root of $L$. Saying, $T ∝ \sqrt{L}$ and $T_1/...
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Spring between two masses: $ΔX$ is halved?
Let's say I have a spring with length of $80$m.
The spring is connected horizontally between two masses (on a table, without friction).
Lets say the string got narrower to $76$m.
Does it mean that $\...
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2
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Does the length of a raft change as the stream bed slides by underneath?
Consider a raft, of length (distance between its two ends, a.k.a. the distance between "bow" and "stern" of the raft) $L_0$.
Now, the river bed slides by quite close underneath the ...
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Is it impossible for anything to touch anything else because of Planck lengths?
Suppose you touch a cube. There would still be a Plank length between your hand and the cube. Does this mean that it is impossible for anything to touch anything, specifically because there is always ...
user318291
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How will the volume of a box change when it is moving?
Suppose, the length, breadth, & height of a box are all equal, it has the shape of a cube and volume $V$. Now, if the box travels at uniform speed $v \gt 0$, then the length $L_0$ will become $L$,
...
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Confusion over length contraction in special relativity
I’m aware that similar questions have been asked numerous times but none of them have helped thus far. When I work through the logic of deriving the formula for length contraction,I keep making an ...
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Technical problem of definition of length of a worldline using a metric $g$
In lecture 10 of this series, the professor defines the notions of speed and length of a curve in a smooth manifold equipped with a metric $g$. These definitions are made between 33:10 and 44:10 and ...
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Error in measurement
A part of my question says "...measured value of L is 20.0 cm known to 1mm accuracy..."; in the solution thereafter $\delta L$ is taken as 1 mm. The least count of the metre scale is 1 mm ...
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How to define "unit spatial length" in general relativity?
Suppose I have a metric with time-independent $g_{\mu\nu}$. Suppose I have a small measuring rod at some spatial position and I define it to be of unit length. Will it still have unit length when it ...
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Changing length of spring
In this formula:
$$F_s = kx$$
what is the force that influences on the length of the spring?
For example I figured out if we pull up a mass attached to a spring with a force, the force of gravity will ...
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1
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What effect does diameter and length of a wire have on the force and extension? [closed]
For example, if wire $A$ has diameter $D$ and length $L$ when a force of $4N$ is applied, it extends to let's say, $0.8mm$.
Another wire $B$ has length and diameter $2L$ and $2D$ respectively. Now, ...
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Length measure in Astronomy
In cosmology, we have a couple of different length measures. Among them, comoving and proper distnlances seem to be good fit to real world use cases in astronomy.
So my quesion is which length measure ...
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Why torque increases with arm length when same force is applied?
Just want to know why the door turns less (less torque) at the point closer to the hinge (point A) than at the outer point at the handle (point B) when the same force is applied. If same force is not ...
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Why is the symmetry of measurements in SR no longer valid in GR?
In special relativity, we know that if an inertial observer $A$, having a relative motion WRT an inertial observer $B$, attributes, say, time dilation and length contraction to respectively $B$'s ...
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Can we measure macroscopic objects with width atom precision?
Can we measure a length of a macroscopic object, like the length of an edge a piece of steel, with atomic level precision, in the sense that we could measure the length of the edge of a crystal ...
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Standard Definition of speed of light and metre
The speed of light is the speed at which lightwaves propagate through different materials. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per ...
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Uncertainty in length measurement
I am trying to measure the length and the uncertainty in length of a fiber optic cable for measuring the speed of light. So far, I have measured it the standard way: Using a standard meter scale. I ...
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Focal length for thick lens [closed]
How can I find the focal length of a thick lens by the method of ray tracing ? I know the ray matrix method but by ray tracing I don't get to an answer.
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Is cross-sectional area over length classified separately from length?
The ratio of cross-sectional area to length (or its reciprocal) appears in several formulas, including those for electrical resistance and capacitance in terms of the resistivity and permittivity. ...
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How length is an invariant in Euclidean space?
The special theory of relativity shows that intervals are invariant under Lorentz transform in the Minkowski space -time.
But how can we prove (any postulates or theory) that the length is an ...
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The length of a string attached to a wall?
I feel really dumb for asking this question. I apologize in advance.
When the example of a string attached to a wall is given to explain waves and the ressonance frequencies, the length of the string ...
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Is length an extensive property?
From my experience, volume, surface and length are extensive properties. Indeed :
the reunion of two cubes of 1 $m^3$ leads to a cube of 2 $m^3$
the reunion of two tiles of 1 $m^2$ leads to a tile ...
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Profile of a platinum-iridium meter bar
The former meter standard, platinum-iridium meter bar, had a specific cross section somewhat resembling mixed variant of letters "X" and "H" with serifs (Image source):
What was the reasoning behind ...
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Definition of a meter and Newtonian law of Gravity
Newtonian law of Gravity:
$$F_g = \frac{m_1 m_2}{l^2} G$$
$$G = 6.7 * 10^{-11} \frac{m^3}{kg * s^2}$$
A meter is defined as:
the length of the path traveled by light in a
vacuum in $1/...
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How is the Length of a Meter Physically Measured?
I have two parts to this question.
First, I understand that the meter is defined as the distance light travels in 1/299,792,458 seconds. But how is this distance actually measured? The second is ...
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How to define approximate meter using primitive to no tools? [closed]
Imagine you've lost somewhere in the wild due to some catastrophic event, and don't have any measurement tools with you. How do you find approximate meter, millimeter, etc. with materials like sticks ...
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Relation Between Power, Distance, Time and Mass
I was calculating something and reached this equation
$${Meter^2 \over Second^3} = {Volt * Ampere \over Kg}$$
Is it correct? Cause if it is... It will tell me I am on the right path.
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Length contraction speed of light
The Special Theory of Relativity tells us that a moving object eg spaceship measures shorter in its direction of motion as its velocity increases.
At the speed of light it would have zero length, but ...
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What is superconducting coherence length?
I'm an electronics student, and don't know much about some physics concepts.
I was studying superconductivity and came to the London equation, Meissner effect and BCS theory.
I kind of understood ...
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If I cut a string, will its length be rational or irrational? [duplicate]
If I cut a string (lets say approximately halfway), will the length of each side (in inches) be rational or irrational?
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How to construct a 12-micron thin layer of powder+epoxy?
Okay, this is more of an engineering tactic question perhaps, but any insight into any possible process will be very, very appreciated. So I'm mixing a powder with epoxy, making a pasty, fluid semi-...
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