Box2D for Flash Games

Defining the Box2D World

Like all worlds, the Box2D World has a gravity , so the first thing you need to do is define world gravity.

1. In your Main function, add the following line:

   var gravity:b2Vec2=new b2Vec2(0,9.81);

   This introduces our first Box2D data type: b2Vec2.

   b2Vec2 is a 2D column vector that is a data type, which will store x and y components of a vector. As you can see, the constructor has two arguments, both numbers, representing the x and y components. This way we are defining the gravity variable as a vector with x=0 (which means no horizontal gravity) and y=-9.81 (which approximates Earth gravity).

   Physics says the speed of an object falling freely near the Earth's surface increases by about 9.81 meters per second squared, which might ...