, . .
. m(t)- t, v(t)- . mv. dt dm dv(dm-). (m+dm)(v+dv). , dt. dmv , dt. t+dt t, dt. Fdt, F , .
(m+dm)(v+dv)+dmv-mv = Fdt
dt . , , dmdv. dm+dm=0 v=v-v .
mdv = vdm + Fdt, dt
m(dv/dt) =v(dm/dt) + F (1)
v(dm/dt) . (1)- .
F=0, mdv = vdm.
, , v. v v.
dv/dm = -(v/m)
v ,
v= - v ò(dm/m) = - v ln(m) + C
. , =0, = m0, 0 = - v ln(m0) + C, = v ln(m0). : v = v ln(m/m0)
m0/m=ev / v . (2)
(2) . (v v << c)
:
, b= v/c.
2.
- . . , .
, , . , , , , . . , .
. sij, ij= - sij . ij, , , .
pij (i¹j), .
|
|
.
, , ,
p11 = p22 = p33 = p (1)
p, , , . (1) , , .
, S1, .
F1, (). , . fii=-piini, ni i- . , , , p11=F1/S1. 11 22 , . , f11= f22 = f /(2)0,5. 22=11. , :
pii=p=F1/S1
.
S2, . , ,
F2 = pS2 = (F1/S1)S2 .
.
, , .
dV=dxdydz FdV (F ).
dydz x p(x,y,z)dydz, p(x+dx,y,z)dydz.
p(x,y,z)dydz p(x+dx,y,z)dydz + Fxdxdydz = 0
p(x,y,z)dxdz p(x,y+dy,z)dxdz + Fydxdydz = 0
p(x,y,z)dxdy p(x,y,z+dz)dxdy + Fzdxdydz = 0
. : - dp/dx + Fx = 0; - dp/dy + Fy = 0; - dp/dz + Fz = 0
, , .
grad p = Ñp = dp/dx ex + dp/dy ey + dp/dz ez, , , ez : - grad p + F = 0.
. .
7.
1.