# Ward's World + McGraw Hill's AccessScience

## Ward's World+MGH Newton's Laws of Motion

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1 Newton's Laws of Motion Article by: Charles J. Goebel, Department of Physics, University of Wisconsin, Madison, Wisconsin. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource that provides immediate, authoritative answers to students' thirst for scientific knowledge on topics such as climate change, virology, pollution, and more. Ward's World and McGraw Hill have partnered to offer educators a no-obligation, free trial subscription to this product. Request your free trial today and discover how valuable AccessScience can be for you and your students. Newton's laws of motion are three fundamental principles that form the basis of classical, or Newtonian, mechanics (Fig. 1). These laws have proved valid for all mechanical problems not involving speeds comparable with the speed of light and not involving atomic and subatomic particles. Newton's laws of motion are as follows: 1. A body not acted on by a force moves with constant velocity, that is, with constant speed in a straight line. 2. The acceleration (rate of change of velocity with time) of a body is proportional to the force acting on it, and inversely proportional to its mass. For precision, if the body is large and irregular or soft, the words "of a body" must be replaced by "of the center of mass of a body." 3. Two bodies exert forces on one another that are equal in magnitude, but opposite in direction (Fig. 2). The first law is merely a special case of the second law when the force is zero. The second law (Fig. 1) is usually stated as "force equals mass multi- plied by acceleration," F = m a, or as "force equals the rate of change of momentum." Although this statement is often regarded as merely defin- ing the force F on a body given its mass m and acceleration a, the fact drawn from experience by Isaac Newton is that a nonzero force always + ward ' s science Key Concepts • Newton's laws of motion comprise three fundamental principles that form the basis of classical mechanics. • The first law of motion states that a body not acted on by a force moves with constant velocity. • The second law of motion states that the acceleration of a body is proportional to the force acting on it, and inversely proportional to its mass. • The third law of motion states that two bodies exert forces on one another that are equal in magnitude, but opposite in direction. Fig. 1: Newton's laws of motion are three fundamental principles of classical mechanics. Newton's second law of motion states that the acceleration (a) of a body is proportional to the force (F) acting on it, and inversely proportional to its mass (m 1 or m 2 ). (Copyright © McGraw-Hill Education)

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