Newtons laws of_motion

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Discusses the 3 laws of motion by Isaac Newton

Discusses the 3 laws of motion by Isaac Newton

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  • 1. Newton’sNewton’s Laws ofLaws of MotionMotionI.I. InertiaInertia II.II. AccelerationAcceleration III.III. Action-ReactionAction-Reaction
  • 2. While most people knowWhile most people know what Newton's laws say,what Newton's laws say, many people do not knowmany people do not know what they mean (or simply dowhat they mean (or simply do not believe what they mean).not believe what they mean).
  • 3. Newton’s Laws of MotionNewton’s Laws of Motion  11stst LawLaw – 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 in motion at constant velocity, unless actedmotion at constant velocity, unless acted upon by an unbalanced force.upon by an unbalanced force.  22ndnd LawLaw – Acc– Acceleration is directlyeleration is directly proportional to Force but inverselyproportional to Force but inversely proportional to mass.proportional to mass.  33rdrd LawLaw –– For every action there is anFor every action there is an equal and opposite reaction.equal and opposite reaction.
  • 4. 11stst Law of MotionLaw of Motion (Law of Inertia)(Law of Inertia) An object at rest will stay atAn object at rest will stay at rest, and an object in motionrest, and an object in motion will stay in motion atwill stay in motion at constant velocity, unless actedconstant velocity, unless acted upon by an unbalanced force.upon by an unbalanced force.
  • 5. 11stst LawLaw  Inertia is theInertia is the tendency of antendency of an object to resistobject to resist changes in itschanges in its velocity:velocity: whether inwhether in motion ormotion or motionless.motionless. These pumpkins will not move unless acted on by an unbalanced force.
  • 6. 11stst LawLaw  Once airborne,Once airborne, unless acted onunless acted on by anby an unbalanced forceunbalanced force (gravity and air(gravity and air – fluid friction),– fluid friction), it would neverit would never stop!stop!
  • 7. 11stst LawLaw  Unless actedUnless acted upon by anupon by an unbalancedunbalanced force, this golfforce, this golf ball would sit onball would sit on the tee forever.the tee forever.
  • 8. Why then, do we observe everyWhy then, do we observe every day objects in motion slowingday objects in motion slowing down and becoming motionlessdown and becoming motionless seemingly without an outsideseemingly without an outside force?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 the frictionless space the moonfrictionless space the moon travels through, are under thetravels through, are under the influence 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 an object What is this unbalanced force that acts on anWhat is this unbalanced force that acts on an object in motion?object in motion?
  • 11. Slide a bookSlide a book across a table andacross a table and watch it slide to a restwatch it slide to a rest position. The bookposition. The book comes to a restcomes to a rest because of thebecause of the presencepresence of a force -of a force - that force being thethat force being the force of friction -force of friction - which brings the bookwhich brings the book to 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 book would continue in motion with the same speedwould continue in motion with the same speed and direction - forever! (Or at least to the endand direction - forever! (Or at least to the end of the table top.)of the table top.)
  • 13. Newtons’s 1Newtons’s 1stst Law and YouLaw and You Don’t let this be you. Wear seat belts.Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resistBecause of inertia, objects (including you) resist changes in their motion. When the car going 80changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your bodykm/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.keeps moving at 80 m/hour.
  • 14. The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck. Slide from www.science-class.net
  • 15. Newton's Second LawNewton's Second Law  If you applyIf you apply moremore force toforce to an object, itan object, it accelerates ataccelerates at a higher rate.a higher rate.
  • 16. 5.2 Newton's Second Law5.2 Newton's Second Law  If the same force isIf the same force is applied to an objectapplied to an object with greater mass,with greater mass, the objectthe object accelerates at aaccelerates at a slower rate becauseslower rate because mass adds inertia.mass adds inertia.
  • 17. 22ndnd LawLaw
  • 18. 22ndnd LawLaw The net force of an object isThe net force of an object is equal to the product of its massequal to the product of its mass and acceleration, or F=ma.and acceleration, or F=ma.
  • 19. 22ndnd LawLaw  When mass is in kilograms and acceleration isWhen mass is in kilograms and acceleration is in 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 to accelerate one kilogram of mass at oneaccelerate one kilogram of mass at one meter/second/second.meter/second/second.
  • 20. Three forms of the second law:Three forms of the second law:
  • 21. 22ndnd Law (F = m x a)Law (F = m x a)  How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per second?  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 unknown  2800 kg-meters/second/second or 2800 N
  • 22. If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.
  • 23. Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces. • We know that objects with different masses accelerate to the ground at the same rate. • However, because of the 2nd Law we know that they don’t hit the ground with the same force. F = maF = ma 98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s F = maF = ma 9.8 N = 1 kg x 9.89.8 N = 1 kg x 9.8 m/s/sm/s/s
  • 24. Check Your UnderstandingCheck Your Understanding  1. What acceleration will result when a 12 N net force1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object?applied to a 3 kg object? A 6 kg object?  2. A net force of 16 N causes a mass to accelerate at a2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/srate of 5 m/s22 . Determine the mass.. Determine the mass.  3. How much force is needed to accelerate a 66 kg3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?skier 1 m/sec/sec?  4. What is the force on a 1000 kg elevator that is4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?falling freely at 9.8 m/sec/sec?
  • 25. 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 the mass.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
  • 26. 33rdrd LawLaw  For every action, there is anFor every action, there is an equal and opposite reaction.equal and opposite reaction.
  • 27. 33rdrd LawLaw According to Newton,According to Newton, whenever objects A andwhenever objects A and B interact with eachB interact with each other, they exert forcesother, they exert forces upon each other. Whenupon each other. When you sit in your chair,you sit in your chair, your body exerts ayour body exerts a downward force on thedownward force on the chair and the chairchair and the chair exerts an upward forceexerts an upward force on your body.on your body.
  • 28. 33rdrd LawLaw There are two forcesThere are two forces resulting from thisresulting from this interaction - a force oninteraction - a force on the chair and a force onthe chair and a force on your body. These twoyour body. These two forces are calledforces are called actionaction andand reactionreaction forces.forces.
  • 29. 5.3 Forces occur in pairs5.3 Forces occur in pairs  The two forces in a pair areThe two forces in a pair are calledcalled actionaction andand reactionreaction..  Anytime you have one, youAnytime you have one, you also have the other.also have the other.  If you know the strength of oneIf you know the strength of one you also know the strength ofyou also know the strength of the other since both forces arethe other since both forces are always equal.always equal.
  • 30. Newton’s Third Law of MotionNewton’s Third Law of Motion If one object exerts a forceIf one object exerts a force on another object, thenon another object, then the second object exerts athe second object exerts a force of equal strength inforce of equal strength in the opposite direction onthe opposite direction on the first objectthe first object ““For every action there isFor every action there is an equal but oppositean equal but opposite reaction”reaction”
  • 31. Action – Reaction PairsAction – Reaction Pairs  Kayak paddle pushes the waterKayak paddle pushes the water back, the water pushes the kayakback, the water pushes the kayak forwardforward  A dog pushes down on theA dog pushes down on the ground, the ground pushes up onground, the ground pushes up on the dog causing it to leap into thethe dog causing it to leap into the airair Other Examples…….Other Examples…….
  • 32. Newton’s 3rd Law in NatureNewton’s 3rd Law in Nature  Consider the propulsion of aConsider the propulsion of a fish through the water. Afish through the water. A fish uses its fins to pushfish uses its fins to push water backwards. In turn,water backwards. In turn, the waterthe water reactsreacts by pushingby pushing the fish forwards, propellingthe fish forwards, propelling the fish through the water.the fish through the water.  The size of the force on theThe size of the force on the water equals the size of thewater equals the size of the force on the fish; theforce on the fish; the direction of the force on thedirection of the force on the water (backwards) iswater (backwards) is opposite the direction of theopposite the direction of the force on the fish (forwards).force on the fish (forwards).
  • 33. 33rdrd LawLaw Flying gracefullyFlying gracefully through the air, birdsthrough the air, birds depend on Newton’sdepend on Newton’s third law of motion. Asthird law of motion. As the birds push down onthe birds push down on the air with their wings,the air with their wings, the air pushes theirthe air pushes their wings up and giveswings up and gives them lift.them lift.
  • 34.  Consider the flying motion of birds. A birdConsider the flying motion of birds. A bird flies by use of its wings. The wings of a birdflies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts bypush air downwards. In turn, the air reacts by pushing the bird upwards.pushing the bird upwards.  The size of the force on the air equals the sizeThe size of the force on the air equals the size of the force on the bird; the direction of theof the force on the bird; the direction of the force on the air (downwards) is opposite theforce on the air (downwards) is opposite the direction of the force on the bird (upwards).direction of the force on the bird (upwards).  Action-reaction force pairs make it possibleAction-reaction force pairs make it possible for birds to fly.for birds to fly.
  • 35. Other examples of Newton’sOther examples of Newton’s Third LawThird Law  The baseball forces theThe baseball forces the bat to the left (anbat to the left (an action); the bat forcesaction); the bat forces the ball to the right (thethe ball to the right (the reaction).reaction).
  • 36. 33rdrd LawLaw  Consider the motion ofConsider the motion of a car on the way toa car on the way to school. A car isschool. A car is equipped with wheelsequipped with wheels which spin backwards.which spin backwards. As the wheels spinAs the wheels spin backwards, they grip thebackwards, they grip the road and push the roadroad and push the road backwards.backwards.
  • 37. 33rdrd LawLaw The reaction of a rocket isThe reaction of a rocket is an application of the thirdan application of the third law of motion. Variouslaw of motion. Various fuels are burned in thefuels are burned in the engine, producing hotengine, producing hot gases.gases. The hot gases push againstThe hot gases push against the inside tube of the rocketthe inside tube of the rocket and escape out the bottomand escape out the bottom of the tube. As the gasesof the tube. As the gases move downward, the rocketmove downward, the rocket moves in the oppositemoves in the opposite direction.direction.
  • 38. Do Action – Reaction ForcesDo Action – Reaction Forces Cancel?Cancel?  If 2 equal act in opposite directions they areIf 2 equal act in opposite directions they are balanced and cancel each other out. There is nobalanced and cancel each other out. There is no movementmovement  Action – Reaction forces do not cancel outAction – Reaction forces do not cancel out because they are acting on 2 different objectsbecause they are acting on 2 different objects
  • 39. Thank You!Thank You!