# Elasticity

## Measuring The Elastic Modulus

The most direct way to determine the elastic modulus of a material is by placing a sample under increasing stresses, and measuring the resulting strains. The results are plotted as a graph, with strain along the horizontal axis and stress along the vertical axis. As long as the strain is small, the data form a straight line for most materials. This straight line is the "elastic region." The slope of the straight line equals the elastic modulus of the material. Alternatively, the elastic modulus can be calculated from measurements of the speed of sound through a sample of the material.

## Resources

### Books

Goodwin, Peter H. Engineering Projects for Young Scientists. New York: Franklin Watts, 1987.

### Periodicals

"A Figure Less Than Greek" Discover 13 (June 1992): 14.

Williams, Gurney, III. "Smart Materials." Omni (April 15, 1993): 42–44+.

Sara G. B. Fishman

## KEY TERMS

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Elastic deformation

—A temporary change of shape or size due to applied force, which disappears when the force is removed.

Elastic modulus

—The ratio of stress to strain (stress divided by strain), a measure of the stiffness of a material.

Plastic deformation

—A permanent change of shape or size due to applied force.

Strain

—The change in dimensions of an object, due to applied force, divided by the original dimensions.

Stress

—The magnitude of an applied force divided by the area it acts upon.