一、定义物体只在重力的作用下,初速度为零的运动,叫做自由落体运动.二、物体做自由落体运动的条件1.只受重力而不受其他任何力,包括空气阻力;2.从静止开始下落.三、自由落体运动的特点1.物体开始下落时是静止的即初速度v=0.如果物体的初速度不为0,就算是竖直下落,也不能算是自由落体.2.物体下落过程中,除受重力作用外,不再受其他任何外界的作用力(包括空气阻力)或外力的合力为0.3.任何物体在相同高度做自由落体运动时,下落时间 First, the definition of the object only under the action of gravity, the initial velocity of zero movement, called free-fall movement. Second, the object to do free-fall movement conditions 1 only by gravity without any other force, including air resistance; From the beginning of the whereabouts of static Third, the characteristics of free-fall movement 1 objects start falling is still the initial velocity v = 0. If the object’s initial velocity is not 0, even if the vertical fall, it can not be free fall.2 In the process of object falling, the force no longer subject to any external force (including air resistance) or external force except the gravity effect is 0.3. When any object makes free-fall movement at the same height, the falling time