Questions tagged [distance]
483 questions
59
votes
7 answers
Photons from stars--how do they fill in such large angular distances?
It would seem that far-away stars are at such a distance that I should be able to take a step to the side and not have the star's photons hit my eye. How do stars release so many photons to fill in such great angular distances?
Shookster
- 1,712
35
votes
2 answers
Why isn't the GPS location calculated from the Schwarzschild metric?
The GPS uses the flat space light propagation formula to calculate the distance from the source (the satellite) to the receiver (observer on Earth):
$$ d=c \cdot \Delta t$$
where $c$ is the speed of light in Minkowski vacuum, $\Delta t$ is the…
label
- 535
35
votes
12 answers
Why does work depend on distance?
So the formula for work is$$
\left[\text{work}\right] ~=~ \left[\text{force}\right] \, \times \, \left[\text{distance}\right]
\,.
$$
I'm trying to get an understanding of how this represents energy.
If I'm in a vacuum, and I push a block with a…
Dominic Roy-Stang
- 493
- 4
- 6
32
votes
3 answers
Why is the work done by a rocket engine greater at higher speeds?
From this comment by orlp:
If I strap a rocket booster to a rocket in space and fire it for one second, then the work provided is much higher when the rocket is flying fast compared to when the rocket was stationary. In both cases the rocket fires…
Pilchard123
- 428
30
votes
6 answers
Is a light year a different distance if measured from a moving object?
The speed of light is absolute, but time is relative. So would a light-year for us on earth be a different distance from a light-year on a different uniformly moving object? Why or why not?
Elliot Chance
- 435
- 4
- 6
26
votes
3 answers
What is the smallest distance possible between two stars?
If two stars of any type were to form near each other, how closely can they form before something prevents them from being two distinct stars?
Alex
- 6,105
25
votes
4 answers
How do astronomers measure the distance to a star or other celestial object?
How do scientists measure the distance between objects in space? For example, Alpha Centauri is 4.3 light years away.
user230
22
votes
5 answers
When we say 'Andromeda galaxy is 2 500 000 light years away from us' do we mean 'now' or in a far past?
When we say 'Andromeda galaxy is 2 500 000 light years away from us do we mean 'now' or in a far past and can this past be calculated easily?
Krešimir Bradvica
- 2,295
20
votes
1 answer
The difference between comoving and proper distances in defining the observable universe
"The radius of the observable universe is estimated to be about 46.5 Gly."
If I understand correctly, it means the most distant object that we can see right now is 46.5 Gly away (at present), but it was 13.7 Gly away at 13.7 billion years ago.…
asmani
- 530
20
votes
9 answers
Why do objects appear smaller when viewed from a distance?
Yes, I know all about perspective (I'm an artist). I even have some basic knowledge of descriptive geometry. I know how it works. My question is more about why it works.
I have a sneaking suspicion it has something to do with the curvature of…
Ricky
- 641
20
votes
2 answers
Why does one get an illusion as moon following him?
When you run or ride bike at night if you observe the moon you feel like he moves along with you as the same speed you are going. Why?
Praveen Kadambari
- 1,663
19
votes
1 answer
Inverse square rule for strong forces
Most of the forces induced by a point particle follows the $1/r^2$ rule. Then why does the strong force not obey it?
STAIN
- 235
16
votes
2 answers
How could scientists know how far a star or galaxy is from us?
How do astronomers measure how far a star (or galaxy) is away from the earth? How would they know that it has taken 13 million years for light to travel in space before it reaches us?
Meysam
- 263
15
votes
11 answers
Is there a proof that the set of real numbers can exactly represent distances?
Mathematicians define real numbers in an abstract way - as an 'ordered field' with 'the least upper bound property'.
In physics, we use real numbers to represent distances. For us to be able to do this, we need to establish the following:
With…
user15740
- 283
14
votes
7 answers
Flat throw vs 45 degree throw of a ball
Why does my sports coach tell me that when I'm fielding I should throw the baseball 'flat' to get the maximum distance? I thought from physics that you get the most distance from throwing at a 45 degree angle? What should I be doing to get the…
user63694
- 317