ydoaPs Posted October 20, 2004 Share Posted October 20, 2004 Why do we use units(m/s) for velocity? Is it because if we don't, then the values are extremely small? If so, wouldn't not using units be good for doing ftl calculations? [math]1s=2.998x10^8m[/math] [math]X\frac{m}{s}=\frac{Xm}{s}=\frac{Xm}{2.998x10^8m}= \frac{X}{2.998x10^8}[/math] Link to comment Share on other sites More sharing options...
Severian Posted October 20, 2004 Share Posted October 20, 2004 That's just the definition of a 'light second'. Link to comment Share on other sites More sharing options...
Callipygous Posted October 20, 2004 Share Posted October 20, 2004 are you asking why we use m/s or why we use units at all? what units we use depends on the magnitude of the speed/distance/whatever that we are measuring. we use units so that when you get a number out the other side you know whether it is acceleration (m/s^2) or velocity (m/s) and you know whether that 1000mph or fps. it makes a difference. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 20, 2004 Author Share Posted October 20, 2004 with m/s, the meters cancel out and leave it with no unit. it also makes the value of the velocity very small. without units, your velocity through spacetime will always be 1. Link to comment Share on other sites More sharing options...
swansont Posted October 20, 2004 Share Posted October 20, 2004 what units we use depends on the magnitude of the speed/distance/whatever that we are measuring. Exactly. If you are going slow, i.e. geologically, you might use cm/year. If you are going fast, terrestrially, you can use Mach numer. If you are going fast, relativistically, you use fractions of c. If you are going FTL, you can make up your units, because it's sci-fi. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 20, 2004 Author Share Posted October 20, 2004 that is not what i am talking about. i am saying that when simplified, m/s doesn't exist. the meters cancel leaving just the number. Link to comment Share on other sites More sharing options...
Callipygous Posted October 20, 2004 Share Posted October 20, 2004 that is not what i am talking about. i am saying that when simplified, m/s doesn't exist. the meters cancel leaving just the number. i dont know what equation that happens in, but if it does i assure you its supposed to. for example, if i am going 20m/h for 20 miles how long does it take me? x=20m/(20m/h) x=20m*(h/20m) x=20mh/20m ("20m"s cancel out) x=1h the miles are gone and im left with my answer, in correct units. Link to comment Share on other sites More sharing options...
Sayonara Posted October 21, 2004 Share Posted October 21, 2004 Any unit for speed is obviously going to be "imaginary" - it's just the rationated value of distance and time taken. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 21, 2004 Author Share Posted October 21, 2004 take any velocityand instead of using seconds, use it's meter equivelent. the meters cancel out, leaving no units. Link to comment Share on other sites More sharing options...
Callipygous Posted October 21, 2004 Share Posted October 21, 2004 take any velocityand instead of using seconds, use it's meter equivelent. the meters cancel out, leaving no units. "instead of using seconds, use it's meter equivelent" what in the world are you talking about? why would you do that? since when is there a "meter equivelent" for seconds? what is the "meter equivelent" for seconds? answer these questions and i might be able to help. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 22, 2004 Author Share Posted October 22, 2004 scince always. i already posted it. Link to comment Share on other sites More sharing options...
Ophiolite Posted October 22, 2004 Share Posted October 22, 2004 scince always. i already posted it.What?Edit:??????? Link to comment Share on other sites More sharing options...
CPL.Luke Posted October 22, 2004 Share Posted October 22, 2004 x=20m/(20m/h) x=20m*(h/20m) x=20mh/20m ("20m"s cancel out) x=1h ** originally posted by calypygous that equation doeln't make sense your deviding a unit of distance by a unit of velocity m/mh is not a real equation thus there is no meter equivelant in time. unless you are trying to define the distance between to objects at different times (which is still questionable) in which case you need to create a new standard measurment this measurement would be good for defining the veloctiy of objects moving ftl. but my original statement about your post is unchanged Link to comment Share on other sites More sharing options...
Callipygous Posted October 22, 2004 Share Posted October 22, 2004 hate to break it to you, but thats how it works. as a matter of fact, im shocked that i would even have to explain this. this is what they teach you in like 5th grade for how to work with units in equations. conversions are done this way. miles per hour to miles per minute: m=miles M=minutes h=hours 100m/h / 60M/h 100m/h * h/60M 100m/1 * 1/60M (h's cancel) 100m/60M (100/60)m/M 1.66m/M 1.66 miles per minute get your facts straight, this is how you do correct units in word problems. although i agree there is no meter equivalent of time. Link to comment Share on other sites More sharing options...
swansont Posted October 22, 2004 Share Posted October 22, 2004 scince always. i already posted it. 1 s = 2.998 X 108m only holds for light, and there is an implicit "c" in there. The correct relationship is c*(1 s) = 2.998 X 108m You don't get to arbitrarily drop units and then do unit analysis. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 22, 2004 Author Share Posted October 22, 2004 [math]c^2={V_x}^2+{V_y}^2+{V_z}^2+{V_t}^2[/math] ok, put 0 for all velocities but time. what is the speed of time? yes class, it is c. now lets use the speed of time for one second. how many meters is it? correct again, 2.998x10^8. Link to comment Share on other sites More sharing options...
Callipygous Posted October 22, 2004 Share Posted October 22, 2004 this is part of the reason i dont belief in space time dialation. if time has a speed then it would be something like sec per ??. i have no idea what it would be for the "??". one thing i can promise you though, time is not measured in meters (i dont care if "the smartest man in the world" says so, so dont bother bringing it up). Link to comment Share on other sites More sharing options...
timo Posted October 22, 2004 Share Posted October 22, 2004 [math]c^2={V_x}^2+{V_y}^2+{V_z}^2+{V_t}^2[/math][...] If at all it´s [math] |v|^2 = c^2 = c^2v_t^2 - v_x^2 - v_y^2 - v_z^2 [/math] (assuming time is measured in seconds and space in meters). It actually IS common to work without units or lenght-dimensions for time' date=' especially in theoretical physics and mathematics. But you should know what you are doing, then . If time has a speed then it would be something like sec per ??. i have no idea what it would be for the "??". [math] v_t [/math] in above would be "coordinate time" per "eigentime". The units depend on what units you chose for them. Link to comment Share on other sites More sharing options...
Bernstein Posted October 22, 2004 Share Posted October 22, 2004 In classical mechanics we use dimensions. The unit of velocity (m/s) is an expression of the relation between the dimensions involved. If it were not for this expression then we would have no basis from which to apply scientific analysis or solution. Link to comment Share on other sites More sharing options...
swansont Posted October 22, 2004 Share Posted October 22, 2004 [math]c^2={V_x}^2+{V_y}^2+{V_z}^2+{V_t}^2[/math] ok' date=' put 0 for all velocities but time. what is the speed of time? yes class, it is c. now lets use the speed of time for one second. how many meters is it? correct again, 2.998x10^8.[/quote'] It's not a valid equation. GIGO. Besides, I get -2.998x108. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 22, 2004 Author Share Posted October 22, 2004 it isn't valid? what happened to all objects travelling through spacetime at c? Link to comment Share on other sites More sharing options...
swansont Posted October 23, 2004 Share Posted October 23, 2004 it isn't valid? what happened to all objects travelling through spacetime at c? The term is c2t2 Link to comment Share on other sites More sharing options...
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