Ball to Ball Collision

Question

I read the page Ball to Ball Collision - Detection and Handling and am a bit confused about the code for resolve_collision. I get everything except what is 1.0f + Constants.restitution? What is 1.0f and what is Constants.restitution?

Answer 1

The 1.0f is the literal for a floating point 1.0. In Java, 1.0 will default to type double, so the author is explicitly making it a float by adding the f flag afterwards.

Constants.restitution supposedly represents the coefficient of restitution, which is usually an e or C_r in physics. This defines how much a ball bounces once it hits the floor or another ball. Though he doesn't show it in the code he provided, it is probably declared somewhere as

public class Constants {
    public static final float restitution = 0.8f;
}

Answer 2

The coefficient of restitution is a number between 0 and 1 that indicates the amount of elasticity in the collision. A 0 means the contacting bodies will stick together, and a 1 means they will bounce off in a perfectly elastic fashion (recovering all their speed).

Try Googling coefficient of restitution and the rest will follow.