Specific volume of substances

[Ry122]

Homework Statement

Must the specific volume of a substance change when it undergoes a change in pressure? Is this true for all substances?

The Attempt at a Solution

obviously this is true in most cases but my question is: are incompressible liquids an exception? When a liquid is attempted to be compressed, does the pressure change? Because if this is the case, then incompressible substances can undergo a change in pressure without the specific volume changing.

 

[Mapes]

Must the specific volume of a substance change when it undergoes a change in pressure? Is this true for all substances?

Yes. So-called "incompressible fluids" are idealizations, materials that undergo shear much more easily than they undergo compression.

 

[Ry122]

But when an incompressible substance undergoes a shear of 3000Kpa for example would the pressure of the substance be no different if it was to reach 3000Kpa through a rise in temperature rather than a change in shear?

 

[Mapes]

But when an incompressible substance undergoes a shear of 3000Kpa for example would the pressure of the substance be no different if it was to reach 3000Kpa through a rise in temperature rather than a change in shear?

I'm not really following you here. Shear stress doesn't cause hydrostatic pressure.

 

[DeeNos]

I can provide a response to this question. The specific volume of a substance is defined as the volume occupied by one unit mass of that substance. Therefore, it is a measure of the density of the substance. In most cases, changes in pressure do affect the specific volume of a substance. This is because pressure and volume have an inverse relationship, known as Boyle's Law. As pressure increases, the volume decreases, and vice versa.

However, there are exceptions to this rule. Incompressible substances, such as liquids, have a very small change in volume when subjected to changes in pressure. This is because the intermolecular forces in liquids are strong enough to resist compression. Therefore, changes in pressure may not significantly affect the specific volume of incompressible substances.

In summary, the specific volume of a substance may change when it undergoes a change in pressure, but this is not always the case. Incompressible substances, such as liquids, may have a very small change in specific volume when subjected to changes in pressure. It is important to consider the properties of a substance when determining how pressure affects its specific volume.