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
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
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
The total translational velocity of the elemental is then the relativistic
sum of (2.44) and v, i.e.
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
|
=
|
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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