acceleration decrease 等唔等於 deceleration??

acceleration 是加速度，一般指物件以每秒計的時間加速移動，加速度下降(acceleration decrease)是物件每秒加速慢下來，即是還在加速。

deceleation是減速，指物件不但沒有加速，相反在減速。

所以，acceleration decrease 不等於 deceleration。

要明白什麼叫accleration 即加速率, 首先要知accleration其實係一個vector
First
Vector, 係乜黎呢？　
係有方向性的，呢個好重要
Then
GIVE you an example
你係條路上面加速向左行，咁你的acceleration係正定係負呢
Ans: 不是正也不是負
因為acceleration係vector, 你要定義左邊個方向係正先
例如，如果我定義剛剛那個situation, i let left direction as positive
hence a is positive, that mean it carry out positive acceleration or negative deceleration
but if i let right direction as negative
a is negative, that mean it carry out positive deceleration or negative acceleration

If you look on the physics point of view, the definition of acceleration is

acceleration = (final velocity - initial velocity)/time taken

In [acceleration decrease], the final velocity is still greater than the initial velocity, though the difference becomes smaller than before. That is, the magnitude of the acceleration is still positvie.

In [decceleration], or sometimes called retardation, the final velocity is smaller than the initial velocity, i.e. the difference of (final velocity - initial velocity) is negative and thus the magnitude of acceleration (i.e. decceleration) is negative.

Hence, acceleration decrease and decceleration means differently in physics.