Newton’s laws of motionpl.n. The three laws proposed by Isaac Newton to describe the motion of a body upon which forces may act and which may exert forces on other bodies, used as the basis of classical mechanics.[After Isaac Newton.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Newton’s laws of motion pl n (General Physics) three laws of mechanics describing the motion of a body. The first law states that a body remains at rest or in uniform motion in a straight line unless acted upon by a force. The second law states that a body’s rate of change of momentum is proportional to the force causing it. The third law states that when a force acts on a body due to another body, then an equal and opposite force acts simultaneously on that body Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Newton’s laws of motion The three laws proposed by Sir Isaac Newton to define the concept of force and describe motion, used as the basis of classical mechanics. The first law states that a body at rest tends to stay at rest, and a body in motion tends to stay in motion at a constant speed in a straight line, unless acted upon by a force. The second law states that the acceleration of a body is equal to the force acting upon it divided by the body’s mass. The third law states that for every action there is an equal and opposite reaction.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.