2.8  Combined Translational and Spin Motions - Relativistic Mass.

When a spinning spherical mass also possesses significant translational motion, the situation becomes a little more complex. Only the mass of the body will be analysed under this condition. Other parameters will exhibit similar characteristics.

Consider a plan view of Fig. 2.1

Picture 4
Fig. 2.4 Spinning Elemental Mass Plus Translational Velocity
From Fig. 2.4 the spin velocity of the elemental mass, normal to the direction of the translational motion is
vn = w¢rsinjcosf
(2.43)
where
w/ is now the spin rate in axes moving translationally with the body.
The spin velocity in the same direction as the translational velocity is
vs = w¢rsinjsinf
(2.44)
The total translational velocity of the elemental is then the relativistic sum of (2.44) and v, i.e.
v* =

v+vs

1+ vvs

c2
(2.45)
The magnitude of the total velocity of the elemental is then
vele = ( vn2 +v*2 )1/2 = ì
í
î
( w¢rsinjcosf )2+ ( v+w¢rsinjsinf )2

æ
è
1+ vw¢rsinjsinf

c2
ö
ø
2

 
ü
ý
þ
1/2


 
(2.46)

The mass of the elemental at rest is given by (2.2) so that the energy mass of the elemental in this scenario is

mele =


m0

æ
è
1- vele2

c2
ö
ø
1/2

 
=


r0 r2sinj df dj dr

ì
í
î
1-
( w¢rsinjcosf )2+ ( v+w¢sinjsinf )2

( 1+[( vw¢rsinjsinf)/( c2)] )2

c2
ü
ý
þ
1/2


 
(2.47)

First, take a relativistic approximation of the second term of the denominator retaining only second order terms. This gives simply

mele =

r0 r2sinj dj df dr

ì
í
î
1- ( w¢rsinjcosf )2

c2
- ( v+w¢rsinjsinf )2

c2
ü
ý
þ
1/2

 
(2.48)

Now take a second relativistic approximation again retaining only second order terms. Thus

mele = r0 r2sinj ì
í
î
1+ 1

2c2
( v2+2vw¢rsinjsinf+w/2r2sin2j ) ü
ý
þ
df dj dr
(2.49)

Integrating (2.49) with respect to f gives the energy mass of the toroid

mtor = ì
í
î
ó
õ
2p

0 
æ
è
r0 r2sinj+ r0 v2r2sinj

2c2
+ r0 w/2r4sin3j

2c2
+ r0 vw/r3sin2jsinf

c2
ö
ø
df ü
ý
þ
 dj dr
(2.50)
Which integrates to
mtor = æ
è
2pr0 r2sinj+ pr0 v2r2sinj

c2
+ pr0 w/r4sin3j

c2
ö
ø
dj dr
(2.51)
Integrating (2.51) with respect to j gives the energy mass of the spherical shell, thus
msh = ì
í
î
ó
õ
p/2

0 
æ
è
4pr0 r2sinj+ 2pr0 v2r2

c2
sinj + 2pr0 w/2r4

c2
sin3j ö
ø
 dj ü
ý
þ
dr
(2.52)
which becomes
msh = æ
è
4pr0 r2+ 2pr0 v2r2

c2
+ 4

3
pr0 w/2r4

c2
ö
ø
dr
(2.53)

Finally integrating (2.53) with respect to r gives the energy mass of the sphere thus

msph = 4pr0 ó
õ
G

0 
æ
è
r2+ 2pr0 v2

c2
r2+ 4

3
pr0 w/2

c2
r4 ö
ø
dr
(2.54)
which yields
msph = 4

3
pr0 G3 æ
è
1+ 1

2
v2

c2
+ 1

5
w/2G2

c2
ö
ø
(2.55)

Converting this to a standard relativistic mass equation via an approximate binomial contraction gives

msph @

m0

æ
è
1- v2

c2
- 2

5
w/2G2

c2
ö
ø
1/2

 
@

m0

æ
è
1- v2

c2
- w/2Ggyr2

c2
ö
ø
1/2

 
(2.56)

For the purpose of determining the energy mass of a spinning spherical body also possessing a linear motion, it therefore appears that, in a second order relativistic approximation, the two separate velocities, each at their own individual mass effective dimension, are simply added together as orthogonal vectors.

Note that because of this combination of the two velocities, the limits to which each can be theoretically increased is reduced. In particular, if v is large enough, it would not be possible to increase w such that wG® c.



R2 Version 1.0.1
Ó P.G.Bass, June 2006

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