Ask A Scientist© General Science Archive

name    Sarah

The physics class at Fatima H.S. would like to find out if gelatin has an
accepted moduli. That is, is there a standard displacement of the surface of
a brick of Jello if a surface stress is applied?
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Hello,

Gelatin is actually a protein, often extracted from animal skin, bone, and 
connective tissues (unknown to some vegetarians).  Gelatin can also be 
obtained from seaweed but it is more expensive and is not normally used in 
food.

When mixed with certain liquids, gelatin proteins trap the liquid in their 
midst and when the mixture is cooled below some temperature, the result is 
a glassy substance also referred to as gelatin. What we discuss here is 
this gelatin.

I do not know, from an engineering standpoint, how gelatin is classified 
.  My  engineering books do not seem to cover it.  Gelatin is not an 
elastomer because it is not made of polymers.  It is a colloidal, however.

Gelatin has a modulus, just as rubber has. But unlike many other substances 
(e.g., metals), its modulus would have a strong velocity dependency. This 
means that you get a different stress-strain curve (whose slope is defined 
as the Young's modulus) depending on the rate of strain.

Actually, gelatin is a great substance to work with and learn from in the 
class room. It is cheap, safe, and very small forces are needed to move it 
around and measure (that is, it has a low modulus). You can measure its 
modulus of elasticity using standard techniques.

I am sure you can find more information on this than I can provide, but 
please let me know if you found information on its classification and 
properties.

Good luck,
AK

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
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