mass times acceleration ( ).
# For every action, there is an equal and opposite reaction. (In other words, whenever one body exerts a force onto a second body, (in some cases, which is standing still) the second body exerts the force back onto the first body. and are equal in magnitude and opposite in direction. So, the body that exerts will be pushed backward.)

Newton's three laws of motion were the first to accurately provide a mathematical model for understanding orbiting bodies in outer space.