This song inlcudes the equation "F = -kx", which is known as "Hooke's Law". It describes the Force F exerted by a spring when it is stretched a distance x from its equilibrium length; k is the spring constant, which is large for a stiff spring, and small for a weak spring. The negative sign shows that the direction of the force exerted by the spring is opposite the direction of the stretch (or compression). For example, if a mass hangs on a spring, and the spring is stretched downward, then x is negative (down), so F = -kx is positive (up).

Any system in equilibrium obeys this force law for small displacements from equilibrium, so this is actually an extremely important equation, despite its simplicity. (For example, the displacements of atoms from their equilibrium positions in a molecule can be accurately modelled using Hooke's law.)

The law was discovered by Robert Hooke (1635-1703), who is also known for coining the word "cell" from his work in microscopy. Hooke's work has not received as much attention as perhaps it should have, partly because he didn't publish it vigorously (the tradition of publishing was not as well established back then), and perhaps because he feuded with Isaac Newton, who outlived him.

--WFS 8/27/05