加速度概念一問

Acceleration is the rate of change of velocity. Since velocity is a vector quantity (which has both magnitude and direction), hence acceleration is also a vector.
Whenever there is a change of the magnitude of velocity (i.e. speed), or direction of velocity, or both magnitude and direction of velocity, there is an acceleration.
如有一部車~以constant speed 圍住一個圈咁轉, 其間係冇改變過speed~只有vol改變, 咁係唔係都係加速度運動???
Yes. There is an acceleration because there is a change of velocity due to a change of the speed direction. Such kind of acceleration is called "centripetal acceleration"(向心加速度).