Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Liquids, Solids, and Compressibility
Name: Jared K.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: Monday, September 30, 2002

How come, when most solids are more dense than liquids, liquids are not compressible, but most solids are?

Both liquids and solids are compressible -- only slightly, but compressible nonetheless. The compressibility of solids is generally smaller (they resist deformation more, because compressibility is defined with an explicit negative sign) than for liquids by ~ 3X. However, there is overlap because other factors are also important.

The compressibility: K = -(dV/dP)/V

varies with temperature, pressure, and other variables, so it is quite difficult to measure. The compressibility of solids, especially single crystals, is even more complicated. Assume the atoms in a crystal have coordinates (x,y,z). The crystal structure is often not isotropic, i.e. the arrangement of atoms/molecules in the 'x', 'y', and 'z' directions is not the same. So an increase in pressure in the 'x' direction results in a DIFFERENT change in volume in the 'y' and 'z' directions. The same is true for the other coordinates. So the compressibility now has NINE components -- Kij where both 'i' and 'j' can equal 'x', 'y', and 'z' -- i.e. components Kxx, Kxy, Kyx,..., Kzz. The term Kxy, for example, measures how the dimensional change in the 'y' direction if I squeeze in the 'x' direction. For some crystals Kxy may not even equal Kyx!! Such nine component arrays are called "tensors" and they have a whole "algebra" that governs their mathematical behavior.

Vince Calder

Liquids are compressible. They just do not compress much compared to gases.

Richard E. Barrans Jr., Ph.D.
Director of Academic Programs
PG Research Foundation, Darien, Illinois

Click here to return to the General Topics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory