Which characteristic does an object with a constant acceleration always have?

Changing velocity

Explanation:

By definition acceleration is the variation of velocity in time. If we do an inverse operation, we will find velocity is the integral of acceleration :

(1)

Solving and taking into account acceleration is constant:

(2)

Being the initial velocity which was the resultant constant from the integration.

From (2) we can see the equation is similar to the equation of the line , where in this case is the slope. This means there is a linear variation in velocity when acceleration is constant.