Expert: Scott Valentine - 8/16/2006

Question
Hi,

I was wondering how deep you would have to sink an egg in water for it to crack under the pressure, I appreciate it would depend on the egg but a rough figure would be great/ interesting!

Cheers!
Joe


Answer
If we assume the egg is filled with a fluid of similar density and characteristic to water, and remove any air (there usually isn't any at first), an egg will not crush under hydrostatic loading. This has to do with the unique shape of the egg as well as the characteristic of the internal fluid.

Pressure at depth is given as the product of density of the fluid, gravity, and the height of the column of fluid above the object. Also keep in mind that pressure is uniformly applied to all sides of the object, and that the direction of force is exactly perpendicular to all surfaces.

Since the egg is continuously curved and filled with fluid, it would require some differential force to cause the egg to crush. Alternatively, if there is a small amount of air, the shell may be deformed over the pocket and then implode at that point. Another event may be the egg contacting some object which applies a nonuniform impulse or force and allows a weakening of the shell.

Newtonian fluids are essentially incompressible, and do not withstand shear forces. So force can only be distributed evenly through still, uniform fluids. In order for fluid to move, it has to have a path of least resistance (e.g., somewhere to go). In an egg, the fluid is trapped, and is being pushed on from all sides evenly, thus it has nowhere to go.

Obvious exceptions are trapped air, deformaties that affect the shell's ability to distribute force, and nonuniform force or pressure.

I hope that helps :)