# Homework Help: Simple harmonic motion of the earth

1. Aug 23, 2009

### monty37

is the rotation of the earth and the revolution of it around sun simple harmonic in nature?
it is periodic but not linear.

2. Aug 23, 2009

### fleem

The orbit is an ellipse, not a circle. So neither the position nor the velocity exactly describe a sine wave, so its not simple harmonic motion.

3. Aug 24, 2009

### Chi Meson

SHM is caused by a restoring force that is linearly proportional to the extension of an object from its equilibrium position. Like a spring, the force that it pushes back with is directly proportional to how much you squeeze it.

The result is periodic motion that is sinusoidal with time.

As a planet moves in orbit, even if it is a perfect circle, there is no movement from or to an equilibrium position. Uniform Circular motion is also periodic, and when you examine the component of motion in a single dimension, this too is sinusoidal. This conveniently allows many of the same formulas to be used when solving advanced problems of both SHM and UCM.

But at its fundamental definition, Uniform Circular Motion is not Simple Harmonic Motion.