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
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