Sir Isaac Newton. Newton s Laws of Motion. Mass. First Law of Motion. Weight. Weight

Transcription

1 Sir Isaac Newton Newton s Laws of Motion Suppleental Textbook Material Pages Born began individual studies Proved universal gravitation Invented the Calculus Reflector telescope 1672 irst Law of Motion Every object continues in its state of rest, or of unifor otion in a straight line, unless it is copelled to change that state by forces ipressed upon it. CONTINUES INERTIA How uch atter Measure of inertia Mass Weight orce upon object due to gravity Proportional to ass Pounds weight Kilogra ass ~2.2 lbs. (in Earth s gravity) Weightass x acceleration of gravity Weight Weightass x acceleration of gravity Mass in kg, gravity is /s 2 Newton force unit of weight 1

2 Mass vs. volue Mass How uch atter Weight orce on the ass Volue How uch space IN CLASS ACTIVITY What is the weight of a two kilogra brick? Weightass x acceleration of gravity Mass2 kg g10/s 2 20 kg Weight(2 kg)(10/s 2 ) s 2 20N Second Law of Motion 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 ass of the object. Means acceleration ~ orce/ass unction of g (acceleration of gravity) Proper units: Different planet different weight for the sae ass Weight is a orce g g Acceleration Change in velocity over tie change in velocity tie orce over ass How can this be? Acceleration Change in velocity over tie change in velocity tie /s s Definition of acceleration 2

3 Acceleration Weight is a orce Change in velocity over tie change in velocity tie /s /s 2 s orce over ass a kg /s 2 /s 2 How it is produced kg Definition of its coponents orce is a vector orce applied to puck Has direction Has agnitude Net force accelerated in direction of su of ipressed forces Added, subtracted, solved for diagonals Sae direction, it goes faster Opposite direction, goes slower At angles, solve with trig or Pythagorean Push 6 Newtons cross-ice Push 8 Newtons up-ice Solve with Pythagorean Theore c 2 a 2 +b 2 3

4 (8N) 2 + (6N) 2 64 N N N 2 c N 2 c 2 100N 2 c 10 N net force on puck c 10N Push 12 Newtons up-ice Push 5 Newtons cross-ice What is net force? (5N) 2 + (12N) 2 25 N N N 2 c 2 (169 N) 2 c (169 N) 2 c 13 N net force Double the force Also need to double the ass Direct proportion constant ratio reely falling objects Boulder vs. feather Gravitational force interaction a a a 4

5 Zero Acceleration Motionless objects Downward force created by gravity Upward force created by surface Zero Acceleration Push down on spring Spring pushes up on you Each olecule of table acts like icroscopic spring pushing up on object Zero Acceleration Cart across roo Net force is zero orce applied pushing frictional force riction Works against forces Opposite direction Not dependent on speed Not dependent on area of contact Only dependent on weight Third Law of Motion Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. orce is an interaction between objects orces of atos within objects are in action reaction pairs No net acceleration due to these olecular forces External force needed to ove object 5

6 orce on object oves it orce by object acts on other things Always equal Action reaction pair Haer exerts force on nail Nail exerts equal force on haer Consider recoil of firear orce on bullet and on rifle the sae Bullet has less ass than rifle Bullet has greater acceleration a a Rifle has less acceleration than the bullet Rocket accelerates upward Recoil fro exhaust gas Birds push down on air Air pushes up on bird ish pushes backward on water Water pushes forward on fish 6

7 Bug vs. Bus If a bug is splatted against the windshield of a bus on the freeway, is the force the bug exerts on the bus the sae as the force the bus exerts on the bug? Justify why the deceleration of the bug is not the sae as the deceleration of the bus with Newton s third law. Suary of laws of otion Newton s irst Law of Motion Object at rest tends to reain at rest Objects in otion tend to reain oving Law of Inertia unction of ass of object Changes in otion occur due to presence of net force acting on object Suary of laws of otion Newton s Second Law of Motion Acceleration proportional to net force a Suary of laws of otion Newton s Third Law of Motion Objects exert equal and opposite forces upon one another have no net force 7