2.3 冲量矩与角动量.ppt

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Johannes Kepler
(1571 - 1630)
ary orbits are ellipses with the sun at one focus. Figure shows the shape and features of an ellipse. ary orbits are not as eccentric as the one drawn here, however.
Kepler’s first law

Kepler’s Laws
引言
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The line joining a to the sun sweeps out equal amounts of area in equal amounts of time. Figure 2 shows this area. If the time interval is equal on both sides, the green area will equal the blue area.
开普勒第二定律Kepler’s second law
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The period of the orbit to the second power is equal to the semi-major axis to the third. The period must be in years and the semi-major axis in astronomical units for this formula to work
Kepler’s third law
Kepler's second and third laws can be stated in ordinary language as:
s move faster near perihelion than near aphelion
s that are close to the sun orbit faster than more distant s.
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开普勒定律
1、行星沿椭圆轨道绕太阳运行,太阳位于椭圆的一个焦点上。行星轨道的偏心率都比较小,很接近圆。
2、对任一行星,它的位置矢量(以太阳中心为参考点)在相等的时间内扫过相等的面积。——面积定律
3、行星绕太阳运动周期T的平方和椭圆轨道的半长轴a的立方成正比,即:
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•
O
匀速直线运动
面积定理成立!!
动量和动能均守恒
动量和动能均发生变化
动量和动能都不是对上述现象做出统一描述的物理量!
问题的提出:
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质点的角动量角动量守恒定律
O
平均角速度Average angular velocity
瞬时角速度Instantaneous angular velocity
It is a Vector
Direction: right-hand rule
Unit: radians per second
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角加速度Angular Acceleration
Constant angular acceleration
Linear motion expression
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质点的角动量Angular momentum of a point mass
Magnitude :
O
Linear momentum
O
m
m
r
r
Angular momentum
Direction: right-hand rule
Rotational inertia: J=mre2
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ponents:
即质点关于三个坐标轴的角动量。
ic energy
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定义合力对参考点O的力矩Torque:
由
=0

d
O
Lever arm
质点的角动量定理