Two moons in orbit, an answer to the first challenge in "Free fall"
This is a great illustration of orbiting planets and gravity. Manipulating the variables, and having all the scripts viewable are a great way to learn this content.
There aren't two moons. The description is meant to read: "A captured comet orbits in two dimensions."
If you like this, you will also like Randy Caton's project from a couple of years ago: "Planet around Sun"
Randy's version allows a deeper exploration of the importance of the time steps, by including a time step variable "dt" that I hid from my own calculations. He also exposes the energy, the area swept out, and the angular momentum to your scrutiny. It was made before Etoys got "function tiles" so it shows what can be achieved with simple arithmetic. More of Randy's projects in mechanics can be found at:
I posed a challenge on page 11. My personal response to the challenge is http://squeakland.org/showcase/project.jsp?id=9739 ("Free fall two")
This is a nice template for building exercises.
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