物理力学基础知识讲座：今日分享六
物理力学基础知识讲座：今日分享六"Common Algorithms for Machine Learning (16)"Today the editor brings youShare interests spread happinessincrease knowledge and leave good news!Dear you this is the new LearningYard Academy
今日分享（六）：如何学好大学物理（3）----刚体力学
亲爱的您，这里是LearningYard新学苑
今天小编为大家带来今日分享（四）
欢迎您的访问！
Share interests spread happiness
increase knowledge and leave good news!
Dear you this is the new LearningYard Academy
Today the editor brings you
"Common Algorithms for Machine Learning (16)"
Welcome your visit！
刚体
刚体：在外力作用下，形状大小不变，而且內部各点相对位置不变的物体。
Rigid body: under the action of external force the shape and size of the object is unchanged and the relative position of the internal points is unchanged.
特点：
1、刚体内任意一对内力功的代数和为0
2、刚体为质点系，故质点系的基本规律可以直接运用于刚体
3、刚体最基本的运动是平动和转动，刚体任何复杂的运动都可分解成平动和转动的合成。
1. The algebraic sum of any pair of internal force work in the rigid body is 0
2. The rigid body is a particle system so the basic laws of the particle system can be directly applied to the rigid body
3. The most basic movement of the rigid body is translation and rotation and any complex movement of the rigid body can be decomposed into the synthesis of translation and rotation
刚体的平动（Translation of rigid body）：
在任意时刻，刚体各质点的位移都是相同的；在任何时刻，各质点的速度和加速度也
相同。
At any time the displacement of each particle of the rigid body is the same; At any one time the velocity and acceleration of each particle also same.
因此刚体内任何一个质点运动，都可代表整个刚体运动。
Therefore any one particle movement in the rigid body can represent the entire rigid body movement.
平动特点（Translational features）：
- 刚体内任意两质元连线在运动过程中始终保持平行
- 运动学范畴内，平动的刚体可视为质点
- 平动刚体运动的轨迹可以是三维的
- Any two-element connection in the rigid body is always parallel during the movement
- In kinematics a flattened rigid body can be considered a particle
- The trajectory of the translational rigid body movement can be three-dimensional
刚体转动（Rigid body rotation）：
刚体运动时，如果刚体各个质点在运动中都绕同一直线圆周运动，这种运动叫做转动，该直线叫做转轴。
When the rigid body is moving if the particles of the rigid body are all moving around the same straight line in motion this movement is called rotation and the straight line is called the shaft
定轴转动特点（Fixed shaft rotation characteristics）：
定轴转动的刚体中各质元在各自的转动平面内绕轴作半径不同的圆周运动。
In a rigid body with a fixed axis rotation each mass element moves around the axis in its own rotation plane with different radii.
刚体定轴转动
定轴转动实例
fixed-axis rotation
刚体上各点都绕同一转轴作不同半径的圆周运动，且在相同时间内转过相同的角度。
Each point on the rigid body moves in a circle of different radii around the same axis of rotation and turns at the same angle in the same time.
角位置（Corner position）：
逆时针转动 θ>0
顺时针转动 θ<0
Turn θ>0 counterclockwise
Turn θ<0 clockwise
角位移（Angular displacement）：
θ=θ（t Δt）- θ(t)
方向（Direction ）：右手螺旋定则 Right-hand spiral rule
角速度（Angular velocity）：
ω=dθ/dt
角加速度（Angular acceleration）：
α=dω/dt
注：刚体上所有质元都具有相同的角位移θ、角速度ω、角加速度α。
Note: All plasmiths on the rigid body have the same angular displacement θ angular velocity ω angular acceleration α.
速度与加速度（Speed and acceleration）：
an=rω ²
at=dv/dt=rdω/dt=rα
类比直线运动：
下节预告----力矩
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翻译来源于谷歌翻译
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