Newton’s Laws of MotionSupplemental Text MaterialPages 300-320Sir Isaac Newton• Born 1642• 1665 began individual studies• Proved universal gravitation• Invented the Calculus• Reflector telescope 1672First 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” = INERTIAMass• How much matter• Measure of inertiaWeight• “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=mass x acceleration of gravity– Mass in kg, g is m/s2• Newton force unit of weightWeightMass vs. volume•Mass– How much matter• Weight– Force on the mass• Volume– How much spaceIN CLASS ACTIVITY• What is the weight of a two kilogram brick?• Weight=mass x acceleration of gravity• Mass=2 kg• g=10m/s2• Weight=(2 kg)(10m/s2)=Ns20m kg 20•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 massmFg =Fmg=Acceleration• Change in velocity over timea = velocity/time• Force over mass• How can this be?mFa =Acceleration• Change in velocity over timea = velocity/timem/ss• Definition of velocityAcceleration• Change in velocity over timea = velocity/time m/s = m/s2s• Force over masskg m/s2= m/s2How it is producedkg Definition of its componentsmFa =Weight is a ForcemFa =maF=Force is a vector• Has direction• Has magnitude• Net force—accelerated in direction of sum of impressed forces• Added, subtracted, solved for diagonalsForce applied to puckAccelerate the Puck• Same direction, it goes faster• Opposite direction, goes slower• At angles, solve with trig or PythagoreanAccelerate the Puck• Push 6 Newtons cross-ice• Push 8 Newtons up-ice• Solve with Pythagorean Theorem c2=a2+b2Accelerate the Puck•82+ 62= 64 + 36 = 100•c2= 100• c = 10 N net force on puckAccelerate 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 N2• c = 13 N net force• Double the force• Also double the mass• Direct proportion—constant ratiomFa =Freely falling objects• Boulder vs. feather=amFmFa =Gravitational force interactionamF==Fma=FmaZero Acceleration• Motionless objects• Downward force created by gravity• Upward force created by surfaceZero Acceleration• Push down on spring• Spring pushes up on you• Each molecule of table acts like microscopic spring pushing up on objectZero Acceleration• Cart across room• Net force is zero• Force applied pushing = frictional forceFriction• Works against forces• Opposite direction• Not dependent on speed• Not dependent on area of contact• Only dependent on weightThird 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 pairsAction—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 objectAction—reaction pairs• Force on object moves it• Force by object acts on other things• Always equalAction—reaction pair• Hammer exerts force on nail• Nail exerts equal force on hammerAction—reaction pairs• Consider recoil of firearm• Force on bullet and on rifle the same• Bullet has less mass than rifle• Bullet has greater acceleration=mF=aFmAction—reaction pairs• Rifle has less acceleration than the bulletAction—reaction pairs• Rocket accelerates upward• Recoil from exhaust gasAction—reaction pairs• Birds push down on air• Air pushes up on bird• Fish pushes backward on water• Water pushes forward on fishSummary 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 objectSummary of laws of motion• Newton’s Second Law of Motion• Acceleration proportional to net forcemFa ≈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
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