Force and Momentum: Newton’s Laws and How to Apply Them

Abstract

In this chapter presents and discusses Newton’s laws, which represent a landmark in the history of science and philosophy in that they, for the first time, replaced descriptions of natural phenomena with explanations in terms of cause and effect. In particular, in the seventeenth century, Kepler’s laws were able to describe planetary motion, but Newton’s laws of motion and Newton’s law of universal gravitation were able to explain planetary motion in terms of fundamental principles. Furthermore, Newton’s laws are applicable far beyond planetary motion. They apply to all motions and lead to many testable predictions that agree extremely well with experiments. This material is foundational for all phenomena that involve motion, including all biologically and medically relevant phenomena that involve motion. This chapter also introduces the concept of momentum and the result that the rate of change of momentum of a collection of particles is equal to the net external force on the collection of particles. When there is no external force, the rate of change of the total momentum of a system of particles is zero. Thus, if there is no external force, the total momentum of a system of particles is constant. We also introduce a stepwise framework—called the 7-step strategy—for always correctly solving problems that involve forces acting on a system.