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Lecture series from Conceptual Physics 8th ed. Newton’s First Law of Motion (56) Inertia is the tendency of things to resist motion. Alias: The law of Push the card out of the way quickly. The coin resists being pushed. Pull quickly on the bottom string and the ball resists being moved. Slam the hammer down and the head resists being stopped… i.e. keeps moving. In Newton’s words….his first law: Every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. INERTIA Let’s define mass and force: MASS= A measure of an object’s inertia, quantity of matter. A “weightless” object has mass. It resists being moved. FORCE= A push or pull. Weight is a force. Mass is measured in units of kilograms, kg Answer p. 60 Newton’s Second Law of Motion p60 The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. (p60) a= F m The unit of force is the Newton, N. Forces are vectors. Note: equilibrium exists! When Acceleration Is Zero – Equilibrium p62 P 64 Static vs Sliding friction. FRICTION When Acceleration Is g – Free Fall p66 For fig 4-13, note that p 67 F = 2F = g m 2m Terminal velocity The person’s weight -- F = mg As velocity increases so does air resistance, R. R mg Mg - R So, a = m R v t mg Newton’s Third Law of Motion p70 Whenever one object exerts a force on a second object, the second object exerts an equal an opposite force on the first. Action Reaction P 72 Because masses are different. The forces are equal. Why aren’t the accelerations equal? The bullet -The gun -- a a = = F F m mThe End