Questions tagged [length]
76 questions
27
votes
6 answers
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 considered one of the seven base units in SI, but since…
Pedro A
- 529
9
votes
1 answer
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 position on the new rubber band? That is, is the…
Number Basher
- 193
9
votes
5 answers
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 these things, but am still wondering: what is…
JayyM
- 91
8
votes
2 answers
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 where the volume is well defined.
Nic Szerman
- 230
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7
votes
3 answers
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)
Paul
- 3,475
5
votes
2 answers
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 of 2 $m^2$
the reunion of two spaghetti of 1 $m$…
yolegu
- 81
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5
votes
2 answers
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($t$).
In the first class, we learned that everything in…
Ben
- 153
5
votes
4 answers
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 corresponding to a proper time between two measurement…
Max Lock
- 85
4
votes
3 answers
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 near the speed of light, does it mean that the meter…
4
votes
1 answer
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 distance traveled by light in a rather short elapse…
niobium
- 754
4
votes
3 answers
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?
Sashank Sriram
- 569
4
votes
2 answers
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 without using the notion of "ruler" or "measuring…
marco trevi
- 279
3
votes
4 answers
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 error which I cannot seem to locate. My logic goes…
P0W8J6
- 421
3
votes
2 answers
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 obviously from an atomic clock, but Wikipedia makes it…
OSUZorba
- 133
2
votes
0 answers
Can a value of "length, in meters" be attributed to a pair of ends which are rigid (but not at rest) to each other?
The definition of the SI base unit "metre" [1] doesn't seem to rule out explicitly that a certain value of "length, in meters" could be attributed to a pair of ends which are rigid to each other, but not at rest to each other.
Consider, therefore,…
user12262
- 4,360