Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

So how fast are we actually moving?

  1. Jan 17, 2007 #1
    Ok I'm having trouble trying to figure something out. There will be a series of questions in this post.

    First of all, how fast exactly is the earth moving? Our average orbital speed is around 30,000 mph (correct me if I'm wrong) around the sun. The sun orbits around the center of our galaxy at approximately 217 km/s, so about 485,415 mph if my math is correct. And right now it's not exactly known, but the Milky Way is approximatley hurling through space at around 552 km/s or 1,234,789 mph So if I add it all together, that's about 1,750,204 mph.

    I guess my question is: Are we really moving that fast, total? I guess it's kind of like being in a car, and you're going 60 mph, but in your perception in the car, you're at 0. If earth is going 30,000 mph and the sun is pulling us around the galaxy center at 485,415 mph, and the galaxy is traveling us at 1,234,789 mph, are we actually moving that fast?

    Another question, is there a such thing as absolute 0 as far as speed is concerned? Is intergalatic space at a "stand still?" Is there any way to determine a 0?

    Also another question. If the speed of light is 186,000 mp/s (roughly) converted to roughly 669,600,000 mph, are we actually already traveling at a fraction of the speed of light?

    Last one!! : When a space ship escapes earth's gravitational pull and is in orbit around the earth in space, is the space ship actually traveling the 1,750,204 + their speed?

    Thanks for whoever answers these questions!
     
  2. jcsd
  3. Jan 17, 2007 #2
    Well, it is not as simple as adding velocities straight off without respect to their directions.

    Your car is not going with a constant velocity in a straight line (curvature of the earth), so it isn't a perfect inertial frame of reference.

    If your question is "Does the Universe move?" the answer is not as simple. How would you show or test it? A scientific hypothesis must be formulated in a way that allows it to be subjected to attempts to falsify it. "Does all books have 200 pages" is one, where as "Does God exist" is not a scientific hypothesis. If it is not a scientific hypothesis, it (generally) does not fall within the realm of science.

    Velocity is relative and there is no special frame of reference where if an object has a relative velocity of 0 m/s with respect to that frame of reference is defined to be at absolute rest.

    You cannot travel faster than the speed of light in any frame of reference according to the theory of relativity because that would demand an infinite amount of force.
     
  4. Jan 17, 2007 #3
    This is impossible find out the TRUE speed of earth. In order to find the true speed of anything you must know the absolute reference frame, but in a universe that is constantly moving how can you??? At best we can only use reference frames from different objects to find speed. Example- you are sitting in front of your computer right now and reading this, relative to the earth you aren't moving at all. Relative to the sun though, you are moving 30,000 mph in an orbit. Then you take the relative value from the center of the milky way and get another value and then the center of the universe and get anouter value. The point is you can't determine the TRUE speed of an object.
     
  5. Jan 17, 2007 #4
    to do a proper vector diagram you need directions
    as earth orbit is at what angle to solar orbit in the galixcy
    and the angle to the galixcy's direction
    unless every vector is lined up it is not a pure addition
    and some motion may cancel

    so what are the vectors victor?
     
  6. Jan 18, 2007 #5

    Jorrie

    User Avatar
    Science Advisor
    Gold Member

    You obviously realize that speed and velocity are relative things. The closest we can come to determining our velocity relative to the universe at large, is to measure the temperature of the cosmic microwave background (cmb) radiation in all directions.

    An observer that measures the average temperature to be the same in all directions can be considered as at rest relative to the cmb. As determined by COBE and WMAP, we are moving in the order of 0.1% of the speed of light relative to the cmb. This is due to the vector-summation of the velocities that you mentioned.

    Jorrie
     
  7. Jan 19, 2007 #6
    How would you go about finding a stationary point in the universe? Or the "centre of the universe"? If we could find a point we knew was motionless or at 0, then we could know our speed relative to this right? Problem is finding that point in the first place? finding a speed relative to the CMB means only that you have found your speed relative to the CMB, not necessarily your true speed relative to a stationary point, you could make the assumption, that the CMB's speed is relative to a stationary point? But how would you prove you were right?
     
  8. Jan 19, 2007 #7

    DaveC426913

    User Avatar
    Gold Member

    I know your intentions are good, but this is misleading.

    It is not simply impossible to find - simply out, there is no such thing as "true speed". It is a meaningless concept.
     
  9. Jan 19, 2007 #8
    Well cosmology is all very confusing to me.

    First we had a wonderful and elegant theory, the general theory of relativity, where motion is relative, time is proper and space-time is defined by mass and energy. Then comes cosmology, where it feels like we are going back to Galilee, now we go back to absolute time, but of course we call it "cosmological time" and we replace the space-time geometry by some extra dimension on which space-time can expand.
    And that is called progress. :tongue2:
     
  10. Jan 19, 2007 #9
    Where did you get that impression from ?
     
  11. Jan 19, 2007 #10

    Jorrie

    User Avatar
    Science Advisor
    Gold Member

    Back to Galilee?

    I know that you were writing this "tongue in the cheek", but I suppose somebody must complain about you calling cosmological time an "absolute time".

    More seriously, I would like to know if the "extra dimension on which space-time can expand" is not applicable to a Schwarzschild vacuum as well? There space curves and as such also contracts and expands, depending on the reference frame, of course.

    Jorrie
     
  12. Jan 19, 2007 #11
    Another question

    I understand the speed is relative to the perspective. Here is another question I have concerning speed in space:

    Let's say you have a space shuttle that launches from earth, and the space ship begins to orbit the earth. The space shuttle's speed is based off of earth's perspective. How could you make the space shuttle come to a "halt" (minus the speed they're going, and the speed of earth's orbit) ? What I'm saying is, let's say the space shuttle decides to let earth whiz by, and halt, and within 1 year the earth will pass back around. So in the space craft's perspective, the earth is traveling at 30,000 MPH.

    How could this be accomplish? Would you have to turn the ship in the opposite direction of the earth's orbit, and begin accelerating at a particular speed? If so, would it not be much less than a year, considering that both the earth and the spaceship are traveling in opposite directions? So how exactly could you accomplish this (assuming that you could stay in one "place" while maintaining around the same proximity to the sun and earth's orbital path.) It's just confusing, because it seems if you use force to try and slow the spacecraft's speed, it's actually moving, if not faster, just in a different direction.
     
  13. Jan 19, 2007 #12

    DaveC426913

    User Avatar
    Gold Member

    If you wanted the shuttle to stop moving wrt to something other than the Earth, for example, the Sun or the celestial sphere, you would have to escape Earth's gravitational field (you'd have to leave orbit) and accelerate in the opposite direction from Earth's movement around the Sun. Eventually, you'd lose the momentum gained by the Earth. As this happens, you'll start falling towards the Sun. You'll need to fire rockets to prevent this.
     
  14. Jan 19, 2007 #13
    Okay your answer cleared that up.

    Why would you start to "lose momentum?" I thought that once and object is in motion, it will stay in motion until acted upon by another force? Would the Sun's gravity be the agent (or force) that causes the lost velocity? Obviously it's what causes the ship to be eventually pulled towards it. But if you're traveling the opposite orbit of earth, it would seem if you're already traveling as fast or faster than earth when you leave orbit, and travel through earth's orbital path backwards, wouldn't that be enough to sustain an orbit around the sun (obviously you would eventually crash into earth.)

    I guess the mass of the spaceship would determine if the spaceship would be pulled toward the sun, or continue it's speed until collison. Is this correct?
     
  15. Jan 20, 2007 #14

    DaveC426913

    User Avatar
    Gold Member

    Sorry, that may have been a confusing statement. What I meant was, if you want to "stop" in the solar system, you will have to activate your rockets to negate the velocity gained by your start from Earth.

    Note that you would need this velocity to stay in orbit - just as Earth does. If you lose this velocity, you'll fall into the sun.

    Wait, when did we start travelling backwards? All we've done is stop. If you wanted to travel backwards, you'd need to keep blasting your rockets.

    But yes, if you did, you'd eventually end up in an orbit the reverse of Earth's. And yes, it would be stable short term.
    No. The mass of the spaceship will not affect its fall. Just like the Space shuttle and a lost wingnut will fall toward Earth at the same rate.
     
  16. Feb 3, 2007 #15


    I think the current speed is 60 seconds a minute, or close to that.

    What was your question?

    (motion is relative, so we can't state that, unless you show us an absolute frame of reference)
     
  17. Feb 3, 2007 #16
    how about this one

    X=Y=Z = 0 at the time of this post for the center of the earth
    in units of your choise [miles, kM, fraction of a light year ect]

    in one years time how far have numbers changed
    adding in all known motion
    [solar orbit around galixcy center + galixcy movement + any other]

    or does nobody like vectors?
     
  18. Feb 4, 2007 #17
    What's your frame of reference????
     
  19. Feb 4, 2007 #18
    earth center at time of post as stated
    aline N to pole and Z axis as commonly done

    basic questions is simple we were at a point and moved
    one year later how far

    no out side frame needed
    we are just tracking earth for one year
     
  20. Feb 5, 2007 #19

    DaveC426913

    User Avatar
    Gold Member

    Ray, if Earth's centre is your frame of reference then after one year Earth has not moved at all. The Earth is still exactly where it was all along wrt to its center and will continue to be so for as long as Earth remains a planet.

    You need to supply a frame of reference OUTSIDE that of what yoiu want to measure, such as the Sun, or the Galactic core or perhaps the local galactic cluster.
     
  21. Feb 5, 2007 #20
    quibbile quibbile quibbile
    the current location of the center not the real center
    I picked that to give a real feal to how far we move in a year
    and picked a year to semi-cancil orbital motion around the sun
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: So how fast are we actually moving?
Loading...