* Mass is a measure of how much matter an object contains.

* Volume is a measure of how much space an object takes up.

If you have two samples of the *same* substance, they'll have the same density (mass per unit volume). This means that if you have the same mass of the substance, it will always occupy the same volume, regardless of its shape or container.

Here's an example to illustrate:

Imagine two identical balloons filled with air. They both have the same mass of air. However, if you squeeze one balloon, you decrease its volume without changing the mass of the air inside. The air itself remains the same substance, but its volume changes due to the pressure applied.

To have two samples of the same substance with different volumes, you'd need to change the amount of the substance. For example, one balloon filled with air and another balloon filled with twice as much air would have the same substance (air) but different volumes.