[extropy-chat] unidirectional thrust

[Dirk Bruere]

Mike Lorrey wrote:

>--- Dirk Bruere <dirk at neopax.com> wrote:
>  
>
>>Mike Lorrey wrote:
>>    
>>
>>>No, Dirk. You don't know what over unity is.
>>>
>>>      
>>>
>>And you do not understand the implications of 'thrust against the 
>>vacuum, fixed stars' etc
>>If we consider a 1kg model car (thrust against the earth) we can
>>convert (neglecting friction and air resistance) say 1MJ of onboard
>>energy to KE resulting in an eventual speed of  around 1400 m/s
>>
>>Let's assume that we have a really good motor that can do all this in
>>ten seconds, for a power input of 100kW. Now, the acceleration is
>>*not uniform* over this time - it starts high and then tails off as
>>the deltaKE increases 
>>
>>Mean acceleration over the first second is going from 0 to 447 m/s
>>for an expenditure of 100kJ ie 447 m/s^2
>>Clearly, if it accelerated at this rate for ten sec then its final 
>>velocity would be 4470 m/s, and it would have a KE some 10MJ - but it
>>doesn't because we have a fixed reference against which we are
>>pushing - the Earth.
>>
>>Now let's translate that to the magic motor that thrusts against 
>>space/universe/whatever.
>>It still accelerates to 447 m/s in the first second, but... why
>>should it not continue at that acceleration? According to relativity
>>one bit of space is the same as another - no preferred frame. So
>>after ten sec with 
>>an expenditure of 1MJ we have a KE (if it hits something in our 
>>reference frame from which we launched it) of 10MJ
>>
>>Sounds pretty over unity to me.
>>    
>>
>
>I don't suppose I have to explain to everyone else how wrong you are. A
>Joule being equal to 1 kg m2 s-2, or 1/4.184 of a calorie, is a unit
>that involves a time term, ergo 100 kJ for 10 seconds is 1 MJ. No over
>unity, Dirk, just bad math and a misunderstanding by you of energy and
>work.
>
>  
>
And what has that to do with the above math which proves you wrong?
Force  = mass.accel
Energy = force.distance
Energy = m.v^2/2
That is all I have used above

I'm afraid it is you who don't understand the imlications of your claim.

-- 
Dirk

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