Understanding Elliptical Orbits

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Hello Folks,

One of the things that my students have the hardest time understanding is elliptical orbits. As one lad said: "Why not circles? Aren't they easier?"

Elliptical orbits come from the effect of gravity on a moving body - and the fact that the force of gravity drops off so rapidly with distance. This also effects the speed of the object in orbit (Kepler's 2nd law of planetary motion and all that...).

This activity is easy to do on a rainy afternoon; all you need is a large sheet of drawing or construction paper, a few pencils and a loop of string. The mathematics are saved for the very end - and they are very simple. (Intro algebra stuff -- nothing worse than a square root in the whole lot. Promise!) You will easily see how gravity and speed relate to an object in orbit and how ellipses work.

For the parents and Scout leaders out there - this also makes a cracking good science project for anyone from 12 years old and up.

Have a go, and let me know how you do.

Dan

Elliptical Orbital Motion - THS 2011.doc