# Chapter 14: N1) Newton's Laws


• 14.1: Forces and Newton's Three Laws
• 14.2: Details on Newton's First Law
According to Newton’s first law (the law of inertia), there must be a cause for any change in velocity (a change in either magnitude or direction) to occur. Inertia is related to an object’s mass. If an object’s velocity relative to a given frame is constant, then the frame is inertial and Newton’s first law is valid. A net force of zero means that an object is either at rest or moving with constant velocity; that is, it is not accelerating.
• 14.3: Details on Newton's Second Law
Newton’s second law of motion says that the net external force on an object with a certain mass is directly proportional to and in the same direction as the acceleration of the object. Newton’s second law can also describe net force as the instantaneous rate of change of momentum. Thus, a net external force causes nonzero acceleration.
• 14.4: Details on Newton’s Third Law
Newton’s third law of motion represents a basic symmetry in nature, with an experienced force equal in magnitude and opposite in direction to an exerted force. Action-reaction pairs include a swimmer pushing off a wall, helicopters creating lift by pushing air down, and an octopus propelling itself forward by ejecting water from its body. Choosing a system is an important analytical step in understanding the physics of a problem and solving it.
• 14.5: Free-Body Diagrams
• 14.6: Vector Calculus
• 14.7: Examples

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