Final answer:
To maintain the original density when there is a change in SFD, volume and pressure must be adjusted inversely according to the ideal gas law; if volume increases, pressure should decrease to preserve density, and vice versa.
Step-by-step explanation:
To maintain the original density when a change in Surface Free Density (SFD) occurs, one must adhere to specific principles informed by the ideal gas law equation PV = NkT. According to this equation, for a given amount of gas (where N is constant), and at constant temperature (T constant), the pressure (P) is inversely proportional to the volume (V). Therefore, to maintain the original density, which is defined as mass per unit volume, we need to balance changes in pressure and volume accordingly.
If the density of a volleyball, for example, were to decrease by approximately 50%, then the volume must increase to double its original value to maintain the same number of particles within the volleyball (assuming no molecules are lost or added). If the volume doubles, then by the inverse proportionality, the pressure must be reduced to half. Similarly, if the density increases, the volume must be reduced proportionately or the pressure must be increased, to maintain the original number of particles per unit volume.