, .
(, , ), , , , , , . , , , . , , , ; .
, , II. ( ) , , :
dA=-d. (12.2)
d F d r (12.2)
F d r =-d. (12.3)
, (r), (12.3) F .
(12.3)
, . . . , , , , . - ( ), .
F =-grad, (12.4)
(i, j, k ). , (12.5), .
grad Ñ. Ñ () , -:
. , , h ,
= mgh, (12.7)
h , 0 = 0. (12.7) , h .
, ( !}. , , , ( h'), =-mgh'.
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(). :
F = -kx,
Fx ; k ( ), , Fx , .
, , . .
Fx=-Fx =kx dA, Fx dx,
dA = Fx dx = kxdx,
. ,
=kx2/2.
, , . .
:
= +,
. . .
************
1 - 2
. . , . , (13.2) ,
d(+) = 0,
+ = E=const, (13.3)
. . . (13.3) : , , , . . .
, ( ), . : .
, . . . , , .
, () . ( ) . , .
. , . , . , , , . , , .
, , , . , . . , , . .
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