of the same length on the Moon would swing more slowly due to the Moon's lower gravitational field strength. Because the value of varies slightly over the surface of the earth, the time period will vary slightly from place to place and will also vary with height above sea level. This approximation is accurate only for small angles because of the expression for angular acceleration being proportional to the sine of the displacement angle: where is the moment of inertia. When is small, and therefore the expression becomes which makes angular acceleration directly proportional and opposite to , satisfying the definition of simple harmonic motion (that net force is directly proportional to the displacement from the mean position and is directed towards the mean position). Scotch yoke A Scotch yoke mechanism can be used to convert between rotational motion and linear reciprocating motion. The linear motion can take various forms depending on the shape of the slot, but the basic yoke with a constant rotation speed produces a linear motion that is simple harmonic in form. See also Notes References External links Simple Harmonic Motion from HyperPhysics Java simulation of spring-mass oscillator Geogebra applet for spring-mass, with 3 attached PDFs on SHM, driven/damped oscillators, spring-mass with friction Classical mechanics Pendulums