As inhabitants of a planet, we are aware of gravity perhaps more than any other force. Gravity, also known as gravitation, will play a part in most of the simulations you’ll build in this book. In fact, you’ve already come across several examples. However, in all the cases you’ve met so far, we’ve dealt with gravity as it exists near the surface of the Earth—as a constant force. It’s now time to take a deeper look at gravity.

Gravity, weight, and mass

Let’s first recap briefly what you already learned about gravity in the previous chapters. If an object has mass m, then Earth exerts a force on it that points vertically downward. The magnitude of this force of gravity is equal to mg, where g is a constant equal to approximately 9.81 m/s ...

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