To maintain consistent density throughout a substance, which of the following factors must remain constant?

To maintain consistent density throughout a substance, mass and volume must remain constant. Density is defined as mass per unit volume (density = mass/volume). Therefore, if either mass or volume changes while the other remains constant, the density will inevitably change as well.

Keeping mass constant means you are not adding or removing material from the substance, and keeping volume constant ensures that the space the material occupies does not change. For instance, if you maintain a fixed amount of substance in a sealed container, both mass and volume remain unchanged, hence the density remains consistent throughout that container.

This concept is essential in aviation maintenance, where maintaining the appropriate density of materials can affect their structural integrity and functionality.