15
:
( /2 ),
, .
dIzz =r ( 2+ 2)dxdy,
dIzz = ra |
a / 2 |
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æ |
a / 2 |
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a / 2 |
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ö |
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ò(x2 |
+ y2 )dxdy = raçç |
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òx2dx + y2 òdx ÷÷dy = |
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− a / 2 |
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è |
− a / 2 |
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−a / 2 ø |
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æ |
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ra |
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ç |
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÷ |
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=raç |
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- (- |
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] + y |
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+ |
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) |
÷dy = ( |
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+ ra |
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y |
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)dy ; |
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8 |
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12 |
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ø |
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a / 2 |
ra4 |
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ra5 |
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ra5 |
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Izz = ò ( |
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+ ra |
y |
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)dy = |
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+ |
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= |
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ra |
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a |
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ma |
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. ( = xx = Iyy ) |
12 |
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12 |
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6 |
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− a / 2 |
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Ixy
dxdy :
dIxy . = -xydm = -rxydV = -rxy2cdxdy , ( dIxy .= –rxy×adxdy)
dy ( . 3) |
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a |
æ |
a |
2 |
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(-a) |
2 ö |
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ç |
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÷ |
( ) |
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Ixy = -2crydy òxdx = -2crç |
2 |
2 |
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÷ydy = 0 , |
− a |
è |
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ø |
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=0.
,
( ),
.
, 2-
, , ( , )
( . 4).
( ) (1,3) (2,4) ,
( )
.
. 4 – .
, <<(a b),
(11 ) (11 ) :
I xx |
= |
1 |
mb2 , |
Iyy |
= |
1 |
ma2 , |
Izz |
= |
1 |
m(a2 + b2 ) = Ixx + Iyy . |
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3 |
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3 |
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3 |
, ,
Nx = Ixwx , Ny = Iywy , Nz = Izwz
( ), N = Iw
N w . N w
.
15
.
,
.
.
.
(xi,yi,zi)
(xi,yi,-zi), z Izx (
) - åmixi zi , ,
z. =0.
, : y = Iyx = yz = Izy = z = Izx = 0.
,
0 (11).
, , ,
( ).
(j, , r). ?
– (7) (8). ,
åmixi2 = åmi yi2 = åmi zi2 ( , (8),
, , z ,
, ). ( yi, zi)
– r , : ri2 = xi2 + yi2 + zi2 .
åmiri2 = åmi xi2 + åmi yi2 + åmi zi2 = 3åmi xi2 ,
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åmixi2 = |
1 |
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åmiri2 . |
( åmiri2 – ?) |
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3 |
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i |
i |
i |
, ,
(j, , r):
I0 = Ixx = Iyy = Izz = åmi (yi2 + zi2 ) = åmi (xi2 + zi2 ) = åmi (yi2 + xi2 ) =
= åmi yi2 + åmi xi2 = 13 åmiri2 + 13 åmiri2 = 23 åmiri2 .
dm ,
r ( 0 R) j ( 0 360o) ( -90 +90 ).
,
( dr): dm = rdV = r× r2dr.
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R |
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R |
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I0 |
= |
òr2dm = |
ròr 2 4pr 2dr = |
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r4p |
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= |
(r× |
pR3 ) × |
R2 = |
× |
mR2 , |
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3 m |
3 0 |
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3 5 |
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I0 |
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mR2 |
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5 |
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( ) |
15
§4. .
,
v w.
v = v +[w¢×ri¢],
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¢ |
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ω′ ri′ – |
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E |
= |
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åmi vi |
= |
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åmi |
(vc + [ |
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×ri ]) |
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= |
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(12) |
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¢ |
¢ |
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¢ |
¢ |
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, ′ , |
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= |
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åmi vc |
+ åmivc ×[ |
×ri ] + |
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åmi ([ |
×ri ]) |
. |
. |
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2 |
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(12) ; 2-
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¢ |
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= vc |
×[ |
¢ |
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¢ |
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¢ |
×0] = 0 , |
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åmivc ×[ |
×ri ] |
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× åmiri ] = vc |
×[ |
(r ¢×m), |
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rc¢= 0 |
¢ . |
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, |
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, |
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: |
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[A×B]×[C×D]=(A×C)(B×D)-(A×D)×(B×C): ( ´ r )2 |
= ( ´ r ) ×( ´ r ) = w2r |
2 |
- ( × r )2 , |
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(w×ri)2=(wxxi+wyyi+wzzi)2, |
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w2 = w2 |
+ w2 |
+ w2 , |
r2 |
= x2 |
+ y2 + z2 . |
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= |
1 |
åmi (w2ri2 - ( ×ri )2 ) ; |
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1 æ |
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2 |
ö |
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= |
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ç(wx + wy |
+ wz )åmi |
(xi |
+ yi |
+ zi ) |
- åmi (wxxi |
+ wy yi |
+ wzzi ) |
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÷ = |
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2 è |
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ø |
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= |
1 |
(w2x Ixx + w2y Iyy + w2z I zz + 2wx wy Ixy |
+ 2wx wz Ixz + 2wy wz I yz ) . |
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(12 ) |
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2 |
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, |
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1. ( ) |
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E |
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(w2 |
+ w2 |
+ w2 ) = |
I0w2 |
. |
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(13) |
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2. |
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( w = w ,0,0), |
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x |
w2 |
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(13 ) |
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3. ,
.
v w ,
: v = v +v ¢ = v +w´r , ri – ,
, , . ,
15
(12) (w´r)2 = (w×r)2 = w2r2 , (12 )
( ),
:
E |
= |
+ E |
= |
mvc2 |
+ |
Ic w2 |
, |
(14) |
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2 |
2 |
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– ,
.
§5. .
.
, :
0
, ,
d :
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I = I0 + md2 . |
(15) |
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w Z (“ ” |
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, – |
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( ), |
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: , |
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. 6 |
( |
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), |
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(14) ) d ,
:
w=j/t Z',
, ( Z') Z
w=j/t, – v =wd ( .
. 6). ,
.
:
E |
= |
Izw2 |
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E |
= |
mvc2 |
+ |
Iz′w2 |
= |
m(w× d)2 |
+ |
I0w2 |
. |
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2 |
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2 |
2 |
2 |
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, :
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I |
w2 |
md2 ×w2 |
I |
w2 |
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z |
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= |
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+ |
0 |
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Þ Iz = md2 + I0 . |
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2 |
2 |
2 |
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, ,
, . ,
0,
.
16
F – , ,
(
). F
, , ,
– .
, ,
.
.
, ( ,
g),
) , ,
. .
. .
F
0.
) . ,
, , ,
, 0:
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F + F + F = 0 F + mg – ma0 = 0, |
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: F – mg – ma0 = 0, |
F = mg + ma0 = m(g + a0).
0 = g, F =2mg – .
10- .
) .
: F + mg – ma0 = 0 F – mg + ma0 = 0, F = m(g – a0).
0 = g, F = 0 – ( ,
.), .
.
§3. ,
1). .
, .
,
. ',
Y′ ( . 1).
') ω.
Z,
16
.
( ) :
a = |
v2 |
(ωR)2 |
2 |
R ; ω=const a |
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4π2 |
R , |
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= |
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= ω |
= |
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R |
T 2 |
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R |
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– .
, '. ,
,
( ) ,
. 1 ”, –
, ,
:
F = mω2R |
F = –F ( –Fn) = – . (4) |
–
. (
) .
ϕ ( . 2)
F = mω2r = 4π2m R cos ϕ ,
T 2
(r=0),
. 2
mg.
2). . .
( ')
:
.
, ,
ω,
( . 3). , ,
v' ( )
( ) – F
. .
) v'
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(R ω, |
v ω |
– |
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, |
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, |
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' ( . 4). |
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ω, |
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R t0 |
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( |
. 4 |
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v0 |
= ωR . |
dt |
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