NEWTON S LAWS OF MOTION Chapter 2 pages 37 53 Review questions 1 5 10 14 17 21 24 30 click for 9 page to print Sir Isaac Newton Born 1642 1665 began individual studies Proved universal gravitation g Invented the Calculus Reflector telescope 1672 Mathematical Principles of Natural Philosophy Principia First Law of Motion Every E object bj t continues ti i its in it state t t off rest t or of uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it CONTINUES INERTIA http www physicsclassroom com mmedia newtlaws cci html Mass How H much h matter tt Measure of inertia Inertia Bird Inertia Coin Inertia Second Law of Motion The 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 Force Means acceleration mass say is proportional to Second Law F a m A l ti iis iinversely l Acceleration A l ti is i directly di tl Acceleration proportional to force proportional to mass Increase forces Force on brick creates acceleration Twice force on brick creates more acceleration Double mass of bricks requires double force to push Acceleration equation F a m If there is double the force Also need to double the mass T maintain To i t i constant t t acceleration l ti Direct proportion constant ratio Acceleration v t Change Ch in i velocity l it over time ti Definition of acceleration Acceleration Change in velocity over time v a t F a m Force over mass AND velocity over time How can this be Acceleration Force causes acceleration Force over mass Solve for the force F a m F ma Freely falling objects Acceleration of gravity is m 9 81 s 2 Use g a constant m 9 9 81 81 s 2 For lecture calculations round d to t 10 m s2 F a m F g m Weight is a Force Function of g acceleration of gravity Proper units Gravity m s2 Mass k kg m kg 2 s Different p planet different weight for the same mass Force F g m mg Fw Weight is a Force g W i h Weight m W i ht mg Weight Increasing mass Neglect air http www physicsclassroom com mmedia newtlaws efff html resistance in this example Galileo s investigation of Galileo s motion Surface area changes air resistance Objects reach terminal velocity due to air resistance In vacuum vacuum this is not a factor Freely falling objects Boulder vs vs feather F a m a F m Boulder has more inertia but not more acceleration so how come it falls faster Air Resistance Acceleration is less than g due to air resistance Friction of air against falling object Air resistance depends on Speed S d Frontal area exposed to air Air Resistance Falling F lli object bj t has h constant t t mass constant t t weight Terminal T i l velocity l i reached h d when h air i resistance matches weight Air resistance function of speed and area Falling object has variable frontal area if you deploy a parachute Air Resistance Parachute increases frontal area area increases air resistanc Increased air resistance balanced with slower speed http www physicsclassroom com mmedia newtlaws sd html Air Resistance Greater air resistance for elephant because it is larger Greater weight because it is more massive More speed required to gain air resistance to overcome the greater weight http www physicsclassroom com mmedia newtlaws efar html Air Resistance Force of air resistance balances greater mass at greater speed Heavier skydiver has greater terminal velocity than lightweight skydiver http www physicsclassroom com mmedia newtlaws efar html Zero Acceleration One case Motionless objects no change in velocity Downward force created by yg gravityy Upward force created by surface Zero Acceleration Another A th case Cart C t crossing i room att constant velocity no change in velocity Net N fforce iis zero Force applied pushing force frictional force Zero Acceleration Push down on spring p g Spring pushes up on you Each molecule of table acts like microscopic spring pushing up on object Friction Works W k against i t forces f Opposite direction Not dependent on speed Not dependent p on area of contact Only dependent on weight Third Law of Motion Whenever Wh one object bj t exerts t a fforce on a second object the second object exerts an equal and opposite force on the first first Force is an interaction between objects Action reaction pairs Force interaction F a m F m a F a m Forces in action reaction action reaction pair are equal Different masses must have different accelerations Action reaction Action reaction pairs Force F on object bj t moves it Force by object acts on other things Always equal Action reaction pair Hammer exerts force on nail Nail exerts equal force on hammer Action reaction pairs Consider firing a F F cannon Force on cannon and on cannonball the same cannonball has less mass than th cannon Cannonball has greater acceleration m F m a Action reaction Action reaction pairs Rifle has less acceleration than the bullet Because it has greater mass Forces are the same Action reaction Action reaction pairs Rocket accelerates upward Recoil from exhaust gas The force that propels a rocket is provided by 1 gravity 2 its exhaust gases 57 3 Newton s laws of motion 4 the atmosphere against which the rocket pushes 19 17 7 1 2 3 4 Action reaction Action reaction pairs Birds push down on air Air p pushes up p on bird Fish pushes backward on water Water pushes forward on fish http en wikipedia org wiki Fish Action reaction Action reaction pairs Forces of atoms within objects are in action p reaction pairs No net acceleration due to these molecular forces External force needed to move object j Summary of laws of motion Newton s First i Law off Motion i Object j at rest tends to remain at rest Objects in motion tend to remain moving Law of Inertia Function of mass of object Changes in motion occur due to presence of net force acting on object Summary of laws of motion Newton s Newton s Second Law of Motion Acceleration proportional to net force F a m Summary of laws of motion Newton s Third hi d Law off Motion Objects exert equal and opposite forces upon one another Action reaction pairs have no net force
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