The tag has no wiki summary.

learn more… | top users | synonyms

15
votes
4answers
1k views

Why are so many forces explainable using inverse squares when space is three dimensional?

It seems paradoxical that the strength of so many phenomena (Newtonian gravity, Coulomb force) are calculable by the inverse square of distance. However, since volume is determined by three ...
6
votes
5answers
554 views

How is distance measured to far away stars and galaxies?

What I need is an accurate description of the methods used to determine the distance to Andromeda. The Parallax method is for nearby objects as I presume. The red shift method applies, but how do you ...
10
votes
0answers
477 views

Why does the moon look bigger at the horizon? [duplicate]

Possible Duplicate: Why does the moon sometimes appear giant and a orange red color near the horizon? Why does the moon look bigger at horizon or skyline than at other times e.g. at ...
3
votes
1answer
467 views

How do I find the initial velocity in this problem?

An X-ray tube gives electrons constant acceleration over a distance of $20\text{ cm}$. If their final speed is $2.0\times 10^7\text{ m/s}$, what are the electrons' acceleration? I know this ...
-1
votes
1answer
261 views

Distance and displacement of an object on a straight line [closed]

I had this homework problem, but don't actually know if what I did is right, or that I even read the problem correctly. Can someone please tell me if this is the right interpretation of the problem ...
1
vote
1answer
1k views

Relation between comoving distance and conformal time?

In cosmology, we have two quantities and I want to understand the physical relation between these two : $\chi = \int_{t_e}^{t_0}c\frac{dt'}{a(t')}$ : the comoving distance with $t_e$ the time at ...
0
votes
1answer
8k views

Finding deceleration and velocity using distance and time

A car is moving down a street with no brakes or gas. The car is slowing due to wind resistance and the effect of friction. The road is flat and straight. The only data I have are timings taken at 100m ...
5
votes
2answers
3k views

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?
4
votes
3answers
341 views

In relativity, what is the difference between a rod that is perpendicular to direction of motion and a rod parallel to the direction of motion?

In Feynman's Lectures on Physics , chapter 15, page 6 he writes about 2 identical, synchronized light signal clocks. These are clocks that consist of a rod (meter stick) with a mirror at each end, and ...
4
votes
2answers
2k views

How do you measure distance to stars within the galaxy?

I know that for close by stars (<50 LY) we can use the parallax effect. And for distant galaxies we use red-shift (& hubble's constant). So how do we measure how far is a star lets say 50,000 ...
5
votes
1answer
1k views

Most accurate ways to find the average distance between stars in Milky way galaxy

I've already posted here on quora. But, I'm not totally sure if it's the most reasonable method. Would anyone care to elaborate on how to find the average distance between stars in a given galaxy ...