多选题速度的大小和方向都不断改变，但加速度的大小和方向都不变的运动是（ ）．A匀速圆周运动B自由落体运动C平抛运动D竖直上抛运动
多选题
速度的大小和方向都不断改变，但加速度的大小和方向都不变的运动是（ ）．
A
匀速圆周运动
B
自由落体运动
C
平抛运动
D
竖直上抛运动
参考解析
解析：
在自由落体运动中，速度方向不变，速度大小不断改变；竖直上抛运动时，速度大小不断改变，但在上升和下落时速度的方向不变．匀速圆周运动速度方向时刻变化，但速度大小不变．可见，上面三种运动都不满足速度大小和方向都不断改变的条件，．平抛运动速度的大小和方向不断变化，而加速度为重力加速度g，大小、方向都不变．
在自由落体运动中，速度方向不变，速度大小不断改变；竖直上抛运动时，速度大小不断改变，但在上升和下落时速度的方向不变．匀速圆周运动速度方向时刻变化，但速度大小不变．可见，上面三种运动都不满足速度大小和方向都不断改变的条件，．平抛运动速度的大小和方向不断变化，而加速度为重力加速度g，大小、方向都不变．
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