my friend said..In physics, acceleration does not mean speeding up.

right?

 

also, why any change in velocity is called an acceleration..

deceleration is a decrease in speed...why deceleration is not much used?

 

thanks

Deceleration is only useful in the context of one dimensional motion, and only with respect to some predefined reference frame. Deceleration is a concept of very limited applicability, and is fully covered by the concept of acceleration in general. Acceleration is any change in velocity.

Deceleration is simply a negative acceleration.

This is an instance of a lay definition not being the same as the scientific definition.