Theoretical mechanics Part3: ) namics
1 Theoretical Mechanics
理论力学
2
Dynamic Introduction 1. The subject of dynamics is the relation between the mechanical motion of a material body and the force acting on it 2 Two models of mechanics 1)A particle is a material body possessing mass, the shape and size of which can be neglected in investigating its motion Examples: When we study a satellites orbit the satellite may be regarded as a particle I. e, satellite- particle a rigid body in translation motion can al ways be treated as a particle I. e, rigid be oay particle 2)A system of particles is a collection of material points in which the position and motion of each particle of the system depends on the position and motion of all the other particles a rigid body is a special system of particles composed of a large number of particles, the distance between any two points of which remains the same during the whole motion. It is also called to be a non-deformable system 3
3 Introduction 1. The subject of dynamics is the relation between the mechanical motion of a material body and the force acting on it. 2. Two models of mechanics. 1) A particle is a material body possessing mass, the shape and size of which can be neglected in investigating its motion. Examples: When we study a satellite’s orbit the satellite may be regarded as a particle. I.e,satellite particle. A rigid body in translation motion can always be treated as a particle. I.e,rigid body particle. 2) A system of particles is a collection of material points in which the position and motion of each particle of the system depends on the position and motion of all the other particles. A rigid body is a special system of particles composed of a large number of particles, the distance between any two points of which remains the same during the whole motion. It is also called to be a non-deformable system
学 引言 一研究对象:研究物体的机械运动与作用力之间的关系 二力学模型: 1质点:具有一定质量而不考虑其形状大小的物体。 例如:研究卫星的轨道时,卫星质点; 刚体作平动时刚体一质点。 2质点系:由有限或无限个有着一定联系 的质点组成的系统。 刚体是一个特殊的质点系,由无数个相互间保持距离 不变的质点组成。又称为不变质点系
4 引 言 一.研究对象： 二.力学模型： 研究物体的机械运动与作用力之间的关系 2.质点系：由有限或无限个有着一定联系 的质点组成的系统。 1.质点：具有一定质量而不考虑其形状大小的物体。 刚体是一个特殊的质点系，由无数个相互间保持距离 不变的质点组成。又称为不变质点系。 例如： 研究卫星的轨道时，卫星 质点； 刚体作平动时,刚体 质点
Dynarnics System of free particles: a system in which the motion of each particle is not restricted by any constraints System of non-free particles refers to a system in which the motion of particle is restricted by constraints A system of particles is the most general abstract model of mechanics including rigid bodies, elastic bodies and fluids Particles dynamics Particle dynamics is the basis of the Dynamics of a system of particles dynamics of a system of particles 4. The fundamental problems of dynamics There are two cases in general. One is to determine the acting forces when the condition of motion is known, the other is to determine the motion of the body when the acting forces are known There are still some additional comprehensive problems. Sometimes part of the forces and part of the motion are known, we have to determine the other part In some cases, the positive forces are known, we should determine the motion firstly, then determine the reaction forces of constraints
5 System of free particles: a system in which the motion of each particle is not restricted by any constraints. System of non-free particles refers to a system in which the motion of particle is restricted by constraints. A system of particles is the most general abstract model of mechanics including rigid bodies, elastic bodies and fluids. 3. Classification of dynamics: Particles dynamics Particle dynamics is the basis of the Dynamics of a system of particles dynamics of a system of particles 4. The fundamental problems of dynamics: There are two cases in general. One is to determine the acting forces when the condition of motion is known, the other is to determine the motion of the body when the acting forces are known. There are still some additional comprehensive problems. Sometimes part of the forces and part of the motion are known, we have to determine the other part. In some cases, the positive forces are known, we should determine the motion firstly, then determine the reaction forces of constraints.