What happens when a substance undergoes a physical change?

A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.

When a substance undergoes a physical change, there is a change of state coupled with the release or absorbtion of energy.

Explanation:

A physical change is a reversible transformation of an object from one form to another that can be observed. In this case, it occurs majorly when an object releases or absorbs a definite amount of energy (e.g heat). It does not affect the chemical composition of the object.

in this image, you can see solar radiation going through ocean water.

no image, but probably absorption

heat the gas and measure the pressure