lots of math in this book....

mechanics is another word of 'real physics'

vector is a quantity that has both magnitude and direction (acceleration)

scalar has only magnitude (density)

in penalty methods, the force at impact is represented by a temporary spring that gets compresed between the objects at the point of impact.

impulse is defined as a force that acts over a very short period of time.

if the collisision is perfectly inelastice, then the two balls of clay will stick to each other and move together at the same velocity after impact collisions in which kinetic energy is conserved are called perfectly elastic.