was a British physicist and physician who introduced Young s
modulus and principle of interference of light. He studied medicine and received his M.D. in
1796. He was appointed Professor of Natural Philosophy at the Royal Institution in 1801, but he
resigned in 1803 as his lectures were disappointing to popular audiences. He joined St. George s
hospital in London as a physician in 1811 and continued there until his death. Young made many
contributions to mechanics. He was the first to use the terms energy and labor expended (i.e.,
work done) for the quantities mv2 and Fx, respectively, where m is the mass of the body, v is its
velocity, F is a force, and x is the distance by which F is moved, and to state that the two terms
are proportional to one another. He defined the term modulus (which has become known as
Young s modulus) as the weight which would double the length of a rod of unit cross section.