Mass is a measure of how much matter an object is made of, and is related to weight. In physics it appears in the equation

acceleration = force / mass

which is one of Newton’s three famous laws. Notice that the larger the mass, the lesser the acceleration given the same force. If you push with the same force on a ’78 Impala and a shopping cart, the cart will accelerate much faster. In the demos so far mass has been left out of the equation:

acceleration = force

which is simply giving mass a value of 1.

In animation, you may want to include mass in the equation so that you could give many objects the same behavior but different masses. For example, it would be useful in making collisions of objects of different sizes look realistic.

When using different masses with gravity, the equation used should be the general gravity equation, not the specialized one given in surface gravity.