M
McMaster student
Guest
Unless there is a real physicist who knows what he is talking about I guess my answer will have to do for now 
in essence, pressure, compression, and stress are very close. compression is the act of doing work against a fluid (gas or liquid), say using a piston, causing its reduction in volume. Pressure is the force the piston feels per unit area from the fluid once you are done compressing. It is also the force you supply per unit area of the piston so that it does not expand again. Stress refers to the same phenomenon but as applied to solid. It is pressure against a solid. However, stress only changes the volume in a very small manner. Most of the stress is accommodated in the solid by deformation (change in its internal molecular potential energies). Stress can be compressive or tensile (compression or tension) and it can be laminar stress (along an axis of the solid just like pulling a spring, or shear stress that gives a torque about the material, like when tearing a paper.
Strain is the response of a solid material to stress. For example, if you pull a tape on width 1 cm with a force of 10 N, your stress is 10N/cm. Now, if the tape is elastic, it will extend by a few mm (say 10 mm), that is the strain. If the relationship between the stress and the strain is linear, we say the material is linear or Hookian (follows Hooke's law of elasticity). Also, if the tape returns to its original status after you have removed the stress, it was in "elastic strain". If not, it was in "plastic strain". Beyond plastic region is material breakage
in essence, pressure, compression, and stress are very close. compression is the act of doing work against a fluid (gas or liquid), say using a piston, causing its reduction in volume. Pressure is the force the piston feels per unit area from the fluid once you are done compressing. It is also the force you supply per unit area of the piston so that it does not expand again. Stress refers to the same phenomenon but as applied to solid. It is pressure against a solid. However, stress only changes the volume in a very small manner. Most of the stress is accommodated in the solid by deformation (change in its internal molecular potential energies). Stress can be compressive or tensile (compression or tension) and it can be laminar stress (along an axis of the solid just like pulling a spring, or shear stress that gives a torque about the material, like when tearing a paper.
Strain is the response of a solid material to stress. For example, if you pull a tape on width 1 cm with a force of 10 N, your stress is 10N/cm. Now, if the tape is elastic, it will extend by a few mm (say 10 mm), that is the strain. If the relationship between the stress and the strain is linear, we say the material is linear or Hookian (follows Hooke's law of elasticity). Also, if the tape returns to its original status after you have removed the stress, it was in "elastic strain". If not, it was in "plastic strain". Beyond plastic region is material breakage