Sun - Cinderella Documentation
Description: The user's guide to the Interactive Geometry Software Cinderella

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# Sun

While the Gravity mode models a constant gravity field that resembles the situation on Earth's surface, the "sun" mode models a central force field that resembles the situation in space. Its gravity field is modeled to simulate the force field of a pointlike mass. This mass is simply added as a usual geometric point in the Add a Point mode. Unlike a free mass, such a sun will not move during a simulation. It only exerts a force on each free mass. The force is bigger for masses that are closer to the sun. The exact relation between the distance dist, the masses involved, and the force is described by the following equation (this is in essence Newton's law of gravity):

force = sunmass * mass / dist²

Free masses with an initial velocity will move in an elliptical, parabolic, or hyperbolic path if they are under the force of a sun. In CindyLab such a situation can be constructed and simulated with a handful of mouse clicks (drawing a sun, drawing a mass with velocity, and starting the animation). The picture below shows the result of such a situation.

A planet orbiting a sun

The situation will become even more interesting if two suns are present. The picture below shows a recorded trace of a planet in the combined force field of two suns.

One planet and two suns

The following two images give an impression of the force field that is caused by one or by two suns to a generic mass. The pictures were generated by the `drawforces()` statement of CindyScript.

### Inspecting Suns