starship-design: Re: New Drive design

[wharton@physics.ucla.edu (Ken Wharton)]

Kyle,

Unfortunately, the saying "If it sounds too good to be true, it probably 
is." applies to Mr. Howard's idea.

>If you swing a mass on a string around in a circle, the mass is pulled
>outward by centrifugal force.  The swinging of the mass in a circle
>caused
>an angular acceleration on the mass pulling it outward.  The angular
>acceleration [feet/second squared] is equal to angular velocity
>[radians/second] squared times the radius [ft.] of swing.  The
>acceleration
>force [lb.] outward equals the mass [lb.sec.sq./ft.] times the angular
>acceleration [ft./sec.sq.].

This is incorrect.  As other members have stated in response to an 
earlier question about centrifugal force, it doesn't exist.  There is no 
force pulling masses on a string outward.  If there was, the masses would 
indeed go outward; they actually go inward, pulled toward the center by 
whatever force is causing the mass to spin around in the first place.  
That inward force is called centripital force, and it is real.  

For the mass on the string example, you are supplying tension on the 
string which pulls the mass inward.  Because the mass is already 
travelling sideways, it comes toward you but also moves to the side, 
forming a perfect circle if the tension is correct.  There's no outward 
force.

Once you stop supplying the tension, the ball does indeed fly away, but 
A) it leaves with the velocity that it had at that moment; no additional 
forces come into play, and B) it doesn't fly Outward; it flies off at a 
tangent.

>If the radius is increased, the angular force is increased in direct
>proportion.  Consider a stationary gear with another gear with the same
>diameter rotating around it.  Place a mass at the outer side of the
>rotating gear.  The locus of the mass as it rotates has a greater radius
>on
>one side than the other.  It can be plotted as x=acos(A)-1)sin(A) and
>y=sin(A) where A equals the angle of rotation.  If four gears are place
>90
>degrees apart,  and the forces from the masses are summed, a constant
>force
>with an amplitude of 2 is produced. The mechanisms could be driven by
>electric
>motors and constant propulsion force and acceleration could be produced.

Of course, you could test this theory by standing on a skateboard and 
swinging a mass around your head, lengthening the string on one side of 
your body and reeling it in on the other side.  If there's a net force 
you can propel yourself in this manner. 

You can't do this, and this is why:  An object with no forces acting on 
it can continue to spin, but it will only spin at its center of mass.  
And, of course, an object spinning at its center of mass will have all of 
its forces balance; it won't start accelerating in any particular 
direction.  No net forces in, no net forces out.

If you want to spin something off-center (as Mr. Howard suggests), you 
need to supply a force.  A centripital force, to be precise, such as the 
earlier tension in a string.  Mr. Howard's idea ignores this force you 
need to put in to spin something off-center, (which, in fact, is the only 
real force in the whole problem).  It exactly balances his proposed 
"acceleration", and in a rotating coordinate system where nothing seems 
to move, there is a net force of zero on the whole system.

Same with magnetic fields; they do no work and can't speed up a proton; 
just change its direction.

Unfortunately, the laws of physics are against us on this one.  If there 
is an easy way to get to the stars we'll find it in new physics, not 
through 400-year old mechanics.

Ken