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NEWTON'S LAWS OF MOTION EXPRESSED AS EQUATIONS
Newton's first law states that an object will move at a constant velocity -- that is, in a straight line at a constant speed -- unless acted upon by an outside force. This is, in other words, the principle of the conservation of momentum. Newton's second law defines force: the force exerted on an object is given by the product of the object's mass and the object's acceleration. Newton's third law states that for every action there is an equal and opposite reaction. Momentum and force are defined mathematically as follows: p = mv (momentum = mass * velocity) F = ma (force = mass * acceleration) So, to summarize: Newton's First Law describes the Conservation of Momentum. Thus, if F = 0, then p = mv is constant. The typical units for velocity is m/s ("meter per second"). The typical units for momentum is kg m/s ("kilogram meter per second"). Newton's Second Law defines force as the change in momentum over time. Thus, if F is not 0, then F = ma. The typical unit for acceleration is m/s2 ("meter per second squared"). The typical unit for force is kg m/s2 ("kilogram meter per second squared"). This unit of force is called a "newton" ("N") in Isaac Newton's honor. Newton's Third Law describes the Reaction Principle. This principle has no straightforward formula, but is a critical tool to evaluate any system of interacting objects. NOTE: Momentum and force are vector quantities - their direction is just as important as their magnitude when computing them. So adding and subtracting momenta and forces requires the use of vector math and trigonometry, if the collisions are not head-on. |