From: zenadsl6186@zen.co.uk   
      
   Parallax  wrote   
      
   > I have a question that may have an obvious answer but I have lost too   
   > many brain cells for it to be obvious to me.   
   >   
   >   
   > isp is given as the thrust produced/quantity of fuel/sec used.   
   > Pounds/(Pounds/sec) gives units of seconds for ISP.  Do the same in   
   > MKS (metric) units and you get:   
   >   
   > Newtons/(Kg/sec)=Kg*m/sec^2/(Kg/sec)=meter*seconds.   
   >   
   > Why do I never see isp expressed in MKS units?   
      
   You forgot g, the attraction due to gravity. It is there to change kgf to   
   Newtons. Isp is simply the time one kilo/lb of fuel will produce one kilo/lb   
   of force.   
      
   The dimension of Isp is time. Makes sense when you think about it, a big Isp   
   will provide the same force for longer.   
      
   The unit of Isp is typically the second.  The second is a MKS unit as well   
   as a unit in many other systems.   
      
   Isp is the force generated times the time the force is generated divided by   
   (g times the fuel used).   
      
   It works out like this:   
      
   Force * time / (g * mass)   
      
   Eg kg m s^-2 * s /(m s^-2 * kg)   
   = kg m s^-2 s m^-1 s^2 kg^-1   
   = s   
      
      
   --   
   Peter Fairbrother   
      
   "It's all right in practice,   
   but in theory it'll never work."   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)