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Newton’s Laws of Motion. Isaac Newton (1642-1727). Father died before he was born Mother remarried & left him with his grandmother Went to Cambridge – earned his keep by working for other students. Black Death – Great Plague. University closed down Newton returned home
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Isaac Newton (1642-1727) • Father died before he was born • Mother remarried & left him with his grandmother • Went to Cambridge – earned his keep by working for other students
Black Death – Great Plague • University closed down • Newton returned home • Began revolutionary advances in optics, mathematics, physics & astronomy
Academic Life • Became Lucasian Professor at Cambridge • First worked on optics • Equated falling apple with “fall” of moon towards Earth • Explained science of moving bodies
Sir Isaac Newton • 1686 published book- Principia • Three laws that relate force to motion
Newton's First Law • An object at rest remains at rest unless acted on by an unbalanced force • -object will not start to move until a push or pull is exerted on it • Ex- golf ball on tee
Newton's First Law of Motion (Part 2) • An object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force • Ex-rocket ship in space- forever!
Newton's First Law of Motion (Friction) • Objects on Earth slow down & stop moving due to friction • Ex- ball stops rolling on grass • Ex- skateboard stops rolling on pavement
Sum up first law • Matter resists any change in motion • Tendency to resist change called inertia • Mass is a measure of inertia • Ex- Baseball= small mass -easy to start and change motion • Ex- Dumpster= large mass - hard to start and change motion
Newton's Second Law of Motion • Part 1-Acceleration Depends on Mass • Acceleration decreases as mass increases • Acceleration increases as mass decreases • Ex- empty versus full shopping cart
Newton's Second Law of Motion • Part 2: Acceleration Depends on Force • Acceleration increases as force increases Ex- large force=fastball pitch Ex-small force= tapping golf ball into hole Acceleration always in direction of force To change direction, exert force in direction you want to go.
Second law expressed mathematically • Relationship of acceleration (a) to mass (m) and force (F) • Units- • a = m/s/s • m= kg • F=kg m/s/s (N)
Equation can be Rearranged • a = F/m • or • F= m X a • or • m=F/a
Newton’s 2nd Law & Falling Objects • Compare apple & watermelon • Larger weight offset by greater inertia • Accelerations due to gravity are same for both
Newton’s Third Law of Motion • Forces act in pairs • Action force exerted by one object = reaction force exerted by 2nd object, but in opposite direction
3rd Law – Think pairs! • Rocket & gases • Push of gas downwards = push of rocket upwards
3rd Law – Think pairs! • Swimmer & water • Force of swimmer pushing on water = force of water pushing back
Momentum • Property of moving objects • Depends on object’s mass & velocity
Greater momentum requires more force to stop or change object’s direction
When objects interact, they may exchange momentum, but total amount of momentum stays the same