If an object undergoes a change in velocity, then it also undergoes a change in:

acceleration

Explanation:

If the velocity is not constant, then there must be a beginning and ending of its velocity. If that is so and there is also a change in time (which there must be) then there is a change in acceleration.

The formula for that is a = (vf - vi)/t

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.