Newton s Laws of Motion Supplemental Textbook Material Pages 300 320 Sir Isaac Newton Born 1642 1665 began individual studies Proved universal gravitation Invented the Calculus Reflector telescope 1672 First Law of Motion 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 CONTINUES INERTIA Mass How much matter Measure of inertia Weight Force upon object due to gravity Proportional to mass Pounds weight Kilogram mass 2 2 lbs in Earth s gravity Weight mass x acceleration of gravity Weight Weight mass x acceleration of gravity Mass in kg gravity is m s2 Newton force unit of weight Mass vs volume Mass How much matter Weight Force on the mass Volume How much space IN CLASS ACTIVITY What is the weight of a two kilogram brick Weight mass x acceleration of gravity Mass 2 kg g 10m s2 20 kg m 2 Weight 2 kg 10m s 20 N s 2 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 mass of the object Means acceleration Force mass Weight is a Force Function of g acceleration of gravity Proper units Different planet different weight for the same mass mg F F g m Acceleration Change in velocity over time a change in velocity time F a m Force over mass How can this be Acceleration Change in velocity over time a change in velocity time m s s Definition of acceleration Acceleration Change in velocity over time a change in velocity time m s2 m s s F Force over mass a m kg m s2 kg m s2 How it is produced Definition of its components Weight is a Force F a m F ma Force is a vector Has direction Has magnitude Net force accelerated in direction of sum of impressed forces Added subtracted solved for diagonals Force applied to puck Accelerate the Puck Same direction it goes faster Opposite direction goes slower At angles solve with trig or Pythagorean Accelerate the Puck Push 6 Newtons cross ice Push 8 Newtons up ice Solve with Pythagorean Theorem c2 a2 b2 Accelerate the Puck 8N 2 6N 2 64 N2 36 N2 100 N2 2 2 2 c c c 100 N c 10 N net force on puck 100 N 10 N 2 Accelerate the Puck Push 12 Newtons up ice Push 5 Newtons cross ice What is net force Accelerate the Puck 5N 2 12N 2 25 N2 144 N2 169 N2 c2 169 N 2 c 169 N 2 c 13 N net force F a m Double the force Also need to double the mass Direct proportion constant ratio Freely falling objects Boulder vs feather F a m a F m Gravitational force interaction F a m F m F a m a 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 molecule of table acts like microscopic spring pushing up on object Zero Acceleration Cart across room Net force is zero Force applied pushing frictional force Friction 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 Force is an interaction between objects Action reaction pairs Action reaction pairs Forces of atoms within objects are in action reaction pairs No net acceleration due to these molecular forces External force needed to move object Action reaction pairs Force on object 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 recoil of firearm Force on bullet and on rifle the same Bullet has less mass than rifle Bullet has greater acceleration F m F m a Action reaction pairs Rifle has less acceleration than the bullet Action reaction pairs Rocket accelerates upward Recoil from exhaust gas Action reaction pairs Birds push down on air Air pushes up on bird Fish pushes backward on water Water pushes forward on fish 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 same as the force the bus exerts on the bug Justify why the deceleration of the bug is not the same as the deceleration of the bus with Newton s third law Summary of laws of motion Newton s First Law of Motion Object 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 Second Law of Motion Acceleration proportional to net force F a m Summary of laws of motion Newton s Third Law of Motion Objects exert equal and opposite forces upon one another Action reaction pairs have no net force
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