Questions tagged [length]

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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 ...
niobium's user avatar
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2 answers
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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 ...
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1 vote
2 answers
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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 ...
Mohammad Javanshiry's user avatar
8 votes
1 answer
808 views

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 ...
Number Basher's user avatar
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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] = ...
Zelkin's user avatar
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3 answers
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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 ...
FMB's user avatar
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108 views

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 ...
sanya's user avatar
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-6 votes
2 answers
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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?
Wanna be a scientist's user avatar
1 vote
0 answers
16 views

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 ...
R Reed's user avatar
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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, ...
ramcdougal's user avatar
2 votes
2 answers
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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 ...
user110391's user avatar
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2 answers
212 views

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 ...
2080's user avatar
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1 answer
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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 ...
Aequitas's user avatar
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What is the proportional relation between effective length $L$ and gravitational acceleration $g$ for a simple pendulum?

The formula of time period of a simple pendulum stands for, T =2π √(L/g). ● If 2π and g remain constant, T would be proportional to the square root of L. Saying, T ∝ √L and T1/T2 would equal √(L1/L2). ...
sidratul muntaha's user avatar
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2 answers
130 views

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 $\...
Ben Shaines's user avatar
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0 answers
63 views

How is time and space defined? [duplicate]

It occurred to me while discussing a different question on this exchange that in order to understand space and time we must first agree on how it's defined in terms of measurement. My current ...
Derek Seabrooke's user avatar
2 votes
2 answers
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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 ...
user12262's user avatar
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1 answer
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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 ...
user avatar
2 votes
2 answers
463 views

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 $L$, ...
tryingtobeastoic's user avatar
3 votes
4 answers
319 views

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 ...
P0W8J6's user avatar
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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 ...
Генивалдо's user avatar
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1 answer
179 views

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 Del L is taken as 1 mm. The least count of the metre scale is 1 mm right? ...
rdev's user avatar
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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 ...
anoniem's user avatar
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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 ...
user283188's user avatar
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1 answer
2k views

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, ...
Virej Dasani's user avatar
2 votes
2 answers
81 views

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 ...
john's user avatar
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2 votes
1 answer
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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 ...
Esbe's user avatar
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0 votes
1 answer
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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 ...
Mohammad Javanshiry's user avatar
1 vote
1 answer
74 views

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 ...
Volker Siegel's user avatar
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6 answers
953 views

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 ...
Gaurav Deval's user avatar
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0 answers
91 views

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 ...
Shaz's user avatar
  • 301
2 votes
1 answer
648 views

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.
Maryam's user avatar
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1 vote
2 answers
269 views

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. ...
hpm's user avatar
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0 votes
1 answer
1k views

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 ...
walber97's user avatar
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1 vote
1 answer
117 views

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 ...
m_botto's user avatar
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5 votes
2 answers
2k views

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 ...
yolegu's user avatar
  • 81
1 vote
1 answer
1k views

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 ...
andselisk's user avatar
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2 votes
1 answer
75 views

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/...
koryakinp's user avatar
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3 votes
2 answers
669 views

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 ...
OSUZorba's user avatar
  • 133
-2 votes
3 answers
245 views

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 ...
baldrs's user avatar
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0 votes
1 answer
1k views

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.
10011101111's user avatar
1 vote
3 answers
2k views

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 ...
jack's user avatar
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9 votes
5 answers
9k views

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 ...
JayyM's user avatar
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0 votes
1 answer
231 views

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?
C A's user avatar
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2 votes
1 answer
148 views

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-...
Betsy's user avatar
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0 votes
1 answer
85 views

Imperial to Metric lenght [closed]

I'm from Metric based country and have an unusual for me imperial notation. Google didn't clear that up for me so I'm asking it here: I have a wall with measures: 10'7-1/4'' What's 7 ? is it tenth of ...
Valery Avsaragov's user avatar
26 votes
6 answers
6k views

Why is the meter considered a basic SI unit if its definition depends on the second?

The metre is the length of the path travelled by light in vacuum during a time interval of 1  ⁄ 299792458 of a second. – 17th CGPM (1983, Resolution 1, CR, 97), source The meter (or metre) is ...
Pedro A's user avatar
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-2 votes
1 answer
1k views

What is the spacetime unit?

So we have a graph of space vs. time, space being $y$, time being $x$. What's the unit for the distance between them? $$\sqrt{(y m)^2+(x s)^2}$$ $$\sqrt{(3m)^2+(4s)^2}$$ $$\sqrt{\frac{(3m)^2}{(3 m)^...
Thomas Olson's user avatar
1 vote
1 answer
35 views

Holograms - interference image, can I tell if the 2nd diode is good for holograms by comparing fringes?

I've created two fringe images - one of a laser diode that's able to make holograms which outputs 5mW. The second laser outputs 20mW and so far I've not been able to make a hologram with it. I had a ...
SarahC's user avatar
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-1 votes
1 answer
194 views

relativity length contraction for twin clock experiment

The question im going to ask is based on scenario given here https://www.scientificamerican.com/article/how-does-relativity-theor/ Only thing that's different is that spacecraft has a length of 1 ...
Gaurav Goyal's user avatar