Questions tagged [length]

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Is length contraction just a rotation in spacetime? [duplicate]

I am trying to understand length contraction in special relativity, in an intuitive way. So I am trying to visualize this phenomenon in the following way, and I would like to know if my example has ...
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Post flagged as duplicate but I still don't know the answer to my question! [migrated]

This post was flagged as duplicate to this but I couldn't understand all the replies very well. Mr John Rennie's reply seems to agree with my initial thought process, but I could be wrong; Is the ...
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Help me understand length contraction in an intuitive way—length contraction as four-dimensional rotations? [duplicate]

I am trying to understand length contraction in special relativity, in an intuitive way. So I am trying to visualize this phenomenon in the following way, and I would like to know if my example has ...
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2 answers
46 views

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). ...
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2 answers
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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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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 ...
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2 votes
2 answers
63 views

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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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 ...
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2 votes
2 answers
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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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2 votes
4 answers
202 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 ...
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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 Del L is taken as 1 mm. The least count of the metre scale is 1 mm right? ...
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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 answer
772 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, ...
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1 vote
1 answer
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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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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 ...
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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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1 vote
1 answer
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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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0 answers
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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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1 answer
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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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1 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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1 vote
1 answer
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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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5 votes
2 answers
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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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3 answers
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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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1 answer
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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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1 vote
3 answers
1k 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 ...
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6 votes
5 answers
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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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1 answer
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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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2 votes
1 answer
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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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1 answer
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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 ...
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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)^...
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1 vote
1 answer
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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 ...
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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 ...
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2 votes
0 answers
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Bandwidth-length product of an optical fiber

A multimode step index fiber has a numerical aperture of 0.2 and a core refractive index of 1.47 . Estimate the bandwidth-length product for the fiber assuming only intermodal dispersion when: (a): ...
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A question about the definition of proper length

As I understand it, the proper length of an object is defined as the length of the object in its rest frame. In terms of the metric it is defined as the length of the spacetime interval between two ...
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How to read this length interval in imperial units?

I am from Europe and I do some research for my thesis. I found this picture, which is very usefull for me, but unfortunately the lengths are in imperial units (for lenght they are using something like ...
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How to calculate the diameter of a moving circle from afar while lacking and knowing some information?

Let's say there is a solid wood wheel with two tires attached at the bottom travelling on a level road towards me while facing me width-wise (as in, the side of it from which you can see its diameter)....
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2 votes
1 answer
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Does limiting to infinity violate laws of physics?

It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$. So if I want to find the limit of ...
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8 votes
2 answers
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Why isn't a meter defined from a kilogram of water?

Why are there different official definitions for a kilogram and for a meter when a meter can be defined by the volume of a kilogram of water? For instance, using the triple point or some other state ...
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5 votes
2 answers
734 views

Can you express mass in other dimensional units?

I'm just started a Physics I course, and while I've paid attention, I'm stuck on one of the first problems: Express mass ($M$) in terms of acceleration($a$), density($D$), area($A$), and time($t$). ...
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4 votes
3 answers
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Proof for Resistance is directly proportional to length and inversely proportional to the area of cross-section?

I have heard that Resistance is directly proportional to length and inversely proportional to area of cross-section. Can someone give me a practical explanation for this?
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4 votes
2 answers
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Where is the logical hole in this reasoning? (special relativity)

I cannot see the problem in the following reasoning, so I'd be glad if you could help me out. The problem is defining a notion of "length" that is consistent with the constancy of the speed of light ...
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1 vote
1 answer
13k views

Does the ratio of magnetic length to geometric length of a bar magnet always remain the same?

It is said that, due to end effects, the assumed poles of a bar magnet are slightly inside the ends of the magnet. The distance between the locations of the assumed poles is called the magnetic length ...
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3 votes
3 answers
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Proper length in GR

What meaning/use is associated with the notion of proper length in general relativity? Do you know an example of any quantity that depends on it? I have so far found statements like "the length ...
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1 answer
869 views

What Is the Physics principle behind dropping a stone into a cup of water?

I have been doing an experiment about relationship between drop height of a stone and the loss of water in the cup it lands in. I found that after dropping the same stone into a cup with the same mass/...
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7 votes
3 answers
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Can I calculate the size of a real object by just looking at the picture taken by a Camera?

Can I calculate the size of a real object by just looking at the picture taken by a Camera? (I think people do that) i dont understand how? (from physics point of view)
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