Thermal Expansion



"Gravitation cannot be held responsible for people falling in love. How on earth can you explain in terms of chemistry and physics so important a biological phenomenon as first love? Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity."

Albert Einstein

th_exp_eqn1

where lsub0 is the "original" length,  delta T is the change in temperature and alpha is the coefficient of linear expansion.  The coefficient of linear expansion is approximtely independent of temperature and is very small, e.g. for steel  alpha = 12 x 10-6 K-1.


th_exp_eqn4

where V0 is the "original" volume and th_exp_eqn5 is the volume coefficient of expansion.

  • Anomalous Expansion of Water
Water is a unique material in many ways.  Without it and its unusual properties life as we know it could not exist.  One of these critical properties is the so-called anomalous expansion.  When heated, most substances expand according to the simple description above, but when heated through the temperature range 0 - 4 0C water contracts (its density increases).

water density

Furthermore, as you are probably aware, when water is cooled and freezes (at 0 0C) the frozen water (ice) expands becoming less dense, causing problems with roads, buildings etc.  This property is very unusual, most substances, on freezing contract rather than expand.  This property of water explains why ice floats.  If this were not the case, the ice created in the winter would sink to the bottom of lakes and oceans and would be insulated from melting in the summer.  After a short time our oceans and lakes would consist of a solid mass of ice with only a thin layer at the surface alternately freezing and melting as the seasons came and went - hardly conducive to the development of life.

What is the difference between a physicist, an engineer, and a mathematician?
If an engineer walks into a room and sees a fire in the middle and a bucket of water in the corner, he takes the bucket of water and pours it on the fire and puts it out.
If a physicist walks into a room and sees a fire in the middle and a bucket of water in the corner, he takes the bucket of water and pours it eloquently around the fire and lets the fire put itself out.
If a mathematician walks into a room and sees a fire in the middle and a bucket of water in the corner, he convinces himself there is a solution and leaves.



 

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu