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- 1. Newton’sNewton’sLaws ofLaws ofMotionMotionI.I. Law of InertiaLaw of InertiaII.II. F=maF=maIII.III. Action-ReactionAction-Reaction
- 2. While most people knowWhile most people knowwhat Newtons laws say,what Newtons laws say,many people do not knowmany people do not knowwhat they mean (or simply dowhat they mean (or simply donot believe what they mean).not believe what they mean).
- 3. Newton’s Laws of MotionNewton’s Laws of Motion 11ststLawLaw – An object at rest will stay at rest,– An object at rest will stay at rest,and an object in motion will stay inand an object in motion will stay inmotion at constant velocity, unless actedmotion at constant velocity, unless actedupon by an unbalanced force.upon by an unbalanced force. 22ndndLawLaw –– Force equals mass timesForce equals mass timesacceleration.acceleration. 33rdrdLawLaw –– For every action there is anFor every action there is anequal and opposite reaction.equal and opposite reaction.
- 4. 11ststLaw of MotionLaw of Motion(Law of Inertia)(Law of Inertia)An object at rest will stay atAn object at rest will stay atrest, and an object in motionrest, and an object in motionwill stay in motion atwill stay in motion atconstant velocity, unless actedconstant velocity, unless actedupon by an unbalanced force.upon by an unbalanced force.
- 5. 11ststLawLaw Inertia is theInertia is thetendency of antendency of anobject to resistobject to resistchanges in itschanges in itsvelocity:velocity:whether inwhether inmotion ormotion ormotionless.motionless.These pumpkins will not move unless acted onby an unbalanced force.
- 6. 11ststLawLaw Once airborne,Once airborne,unless acted onunless acted onby anby anunbalanced forceunbalanced force(gravity and air(gravity and air– fluid friction),– fluid friction),it would neverit would neverstop!stop!
- 7. 11ststLawLaw Unless actedUnless actedupon by anupon by anunbalancedunbalancedforce, this golfforce, this golfball would sit onball would sit onthe tee forever.the tee forever.
- 8. Why then, do we observe everyWhy then, do we observe everyday objects in motion slowingday objects in motion slowingdown and becoming motionlessdown and becoming motionlessseemingly without an outsideseemingly without an outsideforce?force?It’s a force we sometimes cannot see –It’s a force we sometimes cannot see –friction.friction.
- 9. Objects on earth, unlike theObjects on earth, unlike thefrictionless space the moonfrictionless space the moontravels through, are under thetravels through, are under theinfluence of friction.influence of friction.
- 10. There are four main types of friction:There are four main types of friction: Sliding friction:Sliding friction: ice skating Rolling friction:Rolling friction: bowling Fluid friction (air or liquid):Fluid friction (air or liquid): air or water resistance Static friction:Static friction: initial friction when moving anobjectWhat is this unbalanced force that acts on an object in motion?What is this unbalanced force that acts on an object in motion?
- 11. Slide a bookSlide a bookacross a table andacross a table andwatch it slide to a restwatch it slide to a restposition. The bookposition. The bookcomes to a restcomes to a restbecause of thebecause of thepresencepresence of a force -of a force -that force being thethat force being theforce of friction -force of friction -which brings the bookwhich brings the bookto a rest position.to a rest position.
- 12. In the absence of a force of friction, the bookIn the absence of a force of friction, the bookwould continue in motion with the same speedwould continue in motion with the same speedand direction - forever! (Or at least to the endand direction - forever! (Or at least to the endof the table top.)of the table top.)
- 13. Newtons’s 1Newtons’s 1ststLaw and YouLaw and YouDon’t let this be you. Wear seat belts.Don’t let this be you. Wear seat belts.Because of inertia, objects (including you) resist changesBecause of inertia, objects (including you) resist changesin their motion. When the car going 80 km/hour is stoppedin their motion. When the car going 80 km/hour is stoppedby the brick wall, your body keeps moving at 80 m/hour.by the brick wall, your body keeps moving at 80 m/hour.
- 14. 22ndndLawLaw
- 15. 22ndndLawLawThe net force of an object isThe net force of an object isequal to the product of its massequal to the product of its massand acceleration, or F=ma.and acceleration, or F=ma.
- 16. 22ndndLawLaw When mass is in kilograms and acceleration isWhen mass is in kilograms and acceleration isin m/s/s, the unit of force is in newtons (N).in m/s/s, the unit of force is in newtons (N). One newton is equal to the force required toOne newton is equal to the force required toaccelerate one kilogram of mass at oneaccelerate one kilogram of mass at onemeter/second/second.meter/second/second.
- 17. 22ndndLaw (F = m x a)Law (F = m x a) How much force is needed to accelerate a1400 kilogram car 2 meters per second/persecond? Write the formulaWrite the formula F = m x a Fill in given numbers and unitsFill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknownSolve for the unknown2800 kg-meters/second/second or 2800 N
- 18. If mass remains constant, doubling the acceleration, doubles the force. If force remainsconstant, doubling the mass, halves the acceleration.
- 19. Newton’s 2ndLaw proves that different massesaccelerate to the earth at the same rate, but withdifferent forces.• We know that objectswith different massesaccelerate to theground at the samerate.• However, because ofthe 2ndLaw we knowthat they don’t hit theground with the sameforce.F = maF = ma98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/sF = maF = ma9.8 N = 1 kg x 9.89.8 N = 1 kg x 9.8m/s/sm/s/s
- 20. Check Your UnderstandingCheck Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg1. What acceleration will result when a 12 N net force applied to a 3 kgobject? A 6 kg object?object? A 6 kg object? 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s22..Determine the mass.Determine the mass. 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.84. What is the force on a 1000 kg elevator that is falling freely at 9.8m/sec/sec?m/sec/sec?
- 21. Check Your UnderstandingCheck Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg object?1. What acceleration will result when a 12 N net force applied to a 3 kg object?12 N = 3 kg x 4 m/s/s12 N = 3 kg x 4 m/s/s 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s22. Determine the. Determine themass.mass.16 N = 3.2 kg x 5 m/s/s16 N = 3.2 kg x 5 m/s/s 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?66 kg-m/sec/sec or 66 N66 kg-m/sec/sec or 66 N 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? 9800 kg-m/sec/sec or 9800 N9800 kg-m/sec/sec or 9800 N
- 22. 33rdrdLawLaw For every action, there is anFor every action, there is anequal and opposite reaction.equal and opposite reaction.
- 23. 33rdrdLawLawAccording to Newton,According to Newton,whenever objects A andwhenever objects A andB interact with eachB interact with eachother, they exert forcesother, they exert forcesupon each other. Whenupon each other. Whenyou sit in your chair,you sit in your chair,your body exerts ayour body exerts adownward force on thedownward force on thechair and the chairchair and the chairexerts an upward forceexerts an upward forceon your body.on your body.
- 24. 33rdrdLawLawThere are two forcesThere are two forcesresulting from thisresulting from thisinteraction - a force oninteraction - a force onthe chair and a force onthe chair and a force onyour body. These twoyour body. These twoforces are calledforces are called actionactionandand reactionreaction forces.forces.
- 25. Newton’s 3rd Law in NatureNewton’s 3rd Law in Nature Consider the propulsion of aConsider the propulsion of afish through the water. Afish through the water. Afish uses its fins to pushfish uses its fins to pushwater backwards. In turn,water backwards. In turn,the waterthe water reactsreacts by pushingby pushingthe fish forwards, propellingthe fish forwards, propellingthe fish through the water.the fish through the water. The size of the force on theThe size of the force on thewater equals the size of thewater equals the size of theforce on the fish; theforce on the fish; thedirection of the force on thedirection of the force on thewater (backwards) iswater (backwards) isopposite the direction of theopposite the direction of theforce on the fish (forwards).force on the fish (forwards).
- 26. 33rdrdLawLawFlying gracefullyFlying gracefullythrough the air, birdsthrough the air, birdsdepend on Newton’sdepend on Newton’sthird law of motion. Asthird law of motion. Asthe birds push down onthe birds push down onthe air with their wings,the air with their wings,the air pushes theirthe air pushes theirwings up and giveswings up and givesthem lift.them lift.
- 27. Consider the flying motion of birds. A bird flies byConsider the flying motion of birds. A bird flies byuse of its wings. The wings of a bird push airuse of its wings. The wings of a bird push airdownwards. In turn, the air reacts by pushing the birddownwards. In turn, the air reacts by pushing the birdupwards.upwards. The size of the force on the air equals the size of theThe size of the force on the air equals the size of theforce on the bird; the direction of the force on the airforce on the bird; the direction of the force on the air(downwards) is opposite the direction of the force on(downwards) is opposite the direction of the force onthe bird (upwards).the bird (upwards). Action-reaction force pairs make it possible for birdsAction-reaction force pairs make it possible for birdsto fly.to fly.
- 28. Other examples of Newton’sOther examples of Newton’sThird LawThird Law The baseball forces theThe baseball forces thebat to the left (anbat to the left (anaction); the bat forcesaction); the bat forcesthe ball to the right (thethe ball to the right (thereaction).reaction).
- 29. 33rdrdLawLaw Consider the motion ofConsider the motion ofa car on the way toa car on the way toschool. A car isschool. A car isequipped with wheelsequipped with wheelswhich spin backwards.which spin backwards.As the wheels spinAs the wheels spinbackwards, they grip thebackwards, they grip theroad and push the roadroad and push the roadbackwards.backwards.
- 30. 33rdrdLawLawThe reaction of a rocket isThe reaction of a rocket isan application of the thirdan application of the thirdlaw of motion. Variouslaw of motion. Variousfuels are burned in thefuels are burned in theengine, producing hotengine, producing hotgases.gases.The hot gases push againstThe hot gases push againstthe inside tube of the rocketthe inside tube of the rocketand escape out the bottomand escape out the bottomof the tube. As the gasesof the tube. As the gasesmove downward, the rocketmove downward, the rocketmoves in the oppositemoves in the oppositedirection.direction.

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