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Transcript
Newton’s Second Law of Motion Newton’s Second Law Part 1: The net force on an object causes its acceleration. Net Force Net Force, Total Force, Resultant Force ΣF = F1 +F2 + F3 + … Fnet = F1 + F2 + F3 + … Mechanical Equilibrium The resultant force is zero All forces cancel out There is no change in the objects motion Car at Constant Speed ΣF = Normal Force = 2000 N Fa = 50 N Friction = 50 N Weight = 2000 N Net Force Causes Acceleration • To increase the acceleration of an object, you must increase the net force acting on it. • An object’s acceleration is directly proportional to the net force acting on it: acceleration ~ net force (The symbol ~ stands for “proportional to.”) Newton’s Second Law Part 2: The mass of an object resists acceleration. Mass Resists Acceleration • The same force applied to twice as much mass results in only half the acceleration. • The acceleration is inversely proportional to the mass. Newton’s Second LawNet Force causes acceleration, mass resists it. a = Fnet m or Fnet = ma Force is measured in Newtons; 2 (1.00kg)(1.00m/s )= 1 N (Newton) do the math! A car has a mass of 1000 kg. What is the acceleration produced by a force of 2000 N? If the force is 4000 N, what is the acceleration? do the math! How much force, or thrust, must a 30,000-kg jet plane develop to achieve an acceleration of 1.5 m/s2? 10 N 20 N 20 kg a = 0.50 2 m/s right Free Fall Explained How come all objects free fall with the same acceleration? Free Fall Explained As the gravitational force (weight) on an object increases, so does its mass. Net Force causes acceleration and mass resists Mass and Weight Mass is not Weight Mass is the quantity of matter in an object. Weight is the force of gravity on an object. Common Forces Names of some common forces Tension Normal/Support Force Gravitational Force/Weight Friction Applied force Free-Body Diagrams Normal N mg mg You can safely hang from a clothesline hanging vertically, but you will break the clothesline if it is strung horizontally.