革擦大寧 但博学求回新 South chi na Agricul tural Uni versity Chap 2 Kinetics of particles L NEWTON'S LAW 2. WORK and energy 3. MOMENTUM 26
D e p. p h y sic s D e p. p h y sic s D e p. p h y sic s 26 Chap.2 Kinetics of particles 1.NEWTON’S LAW 2. WORK and ENERGY 3. MOMENTUM
革擦大寧 但博学一求宣倒新 South chi na Agricul tural Uni versity 1.NEWTONS LAW Newton's first law An object at rest remains at rest and an object in motion continues in motion with constant velocity(that s, constant speed in a straight line)unless it experiences a net external force 。 Newton' s Third law If two bodies interact, the magnitude of the force exerted on body I by body 2 is equal to the magnitude of the force exerted on body 2 by body 1, and these two forces are opposite in direction
D e p. p h y sic s D e p. p h y sic s D e p. p h y sic s 27 1.NEWTON’S LAW l Newton’s First Law An object at rest remains at rest, and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line) unless it experiences a net external force. l Newton’s Third Law If two bodies interact, the magnitude of the force exerted on body 1 by body 2 is equal to the magnitude of the force exerted on body 2 by body 1, and these two forces are opposite in direction
③举南演掌大 但博学一求宣倒新 South chi na Agricul tural Uni versity Newton's second law The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. The direction of the acceleration is the direction of the resultant force dm dp d(mv) m+卩 28
D e p. p h y sic s D e p. p h y sic s D e p. p h y sic s 28 l Newton’s Second Law The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. The direction of the acceleration is the direction of the resultant force. dt dP F dt d(mv) ma dt dv m dt dm v dt dv m
③举南演掌大 但博学求回新 South chi na Agricul tural Uni versity F=m dt Note Conditions of the law 1. Macroscopic system with low velocity 2 Inertial reference frame
Dep. physics Dep. physics Dep. physics 29 Note:Conditions of the law 1.Macroscopic system with low velocity 2.Inertial reference frame 2 2 dv d r F m m dt dt
(力落掌大孝 信德博学 求创案 South chi na Agricul tural Uni versity (例)一质量为m的物体,以v的初速度沿与水平方向成a角的方向抛 出,空气的阻力与物体的动量成正比,比例系数为k,求物体的运动轨迹。 解:建立坐标系如图 Y kmy m 研究对象“m受力mg,kmv 运动方程:(矢量方程) d mg X m8 t km v =m dt 运动方程的分量式 动画 lt m J 30
D e p. p h y sic s D e p. p h y sic s D e p. p h y sic s 30 (例)一质量为 m 的物体，以 v 的初速度沿与水平方向成 角的方向抛 出，空气的阻力与物体的动量成正比，比例系数为 k ，求物体的运动轨迹。 mg kmv m mg kmv , 解：建立坐标系如图 研究对象“ m”受力 运动方程： （矢量方程） 运动方程的分量式： x : kmv x y : mg kmv y dt dv m x dt dv m y m g km v dt d v m 动画