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Newtons Law of Motion

- 1. Newton’s Laws of Motion I. Law of Inertia II. F=ma III. Action-Reaction
- 3. While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean).
- 4. Background Sir Isaac Newton (1643-1727) was an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion. Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.
- 5. “If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent.” -Sir Isaac Newton
- 6. Forces and Motion Forces can create cha nges in motion (accel eration or deceleratio n).
- 7. Definition of a Force A force is a p ush or a pull.
- 8. Balanced Force A force that prod uces no change i n an object’s mo tion because it is balanced by an e qual yet opposite force.
- 9. Unbalanced Forces Are forces that result in an ob ject’s motion b eing changed. +
- 10. Motion can be described as : A change in an obje ct’s position.
- 11. Newton’s Laws of Motion 1st Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. 2nd Law – Force equals mass times acceleration. 3rd Law – For every action there is an equal and opposite reaction.
- 12. Vocabulary 1. Friction- a force that opposes motion between 2 objects that are touching 2. Inertia-tendency of all objects to stay at rest or in motion 3. Mass- the amount of matter an object is made of
- 13. 1st Law of Motion (Law of Inertia) An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.
- 15. 1st Law Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move unless acted on by an unbalanced force.
- 16. Examples of Law of Inertia The body moves to the side when a car makes a sharp turn. Seat belts tightening in a car when it stops quickly. A ball rolling down a hill will continue to roll unless friction or another force stops it. If pulled quickly, a tablecloth can be removed from underneath of dishes
- 17. Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see – friction.
- 18. Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction.
- 19. There are four main types of friction: Sliding friction: ice skating Rolling friction: bowling Fluid friction (air or liquid): air or water resistance Static friction: initial friction when moving an object What is this unbalanced force that acts on an object in motion?
- 20. Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a rest position.
- 21. In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)
- 22. Newtons’s 1st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.
- 24. Examples of Newton’s 1st Law of Motion 1. Car suddenly stops and you strain against the seat belt 2. Car turns left and you appear to slide to the right 3. The difficulty of pushing a car that won’t start
- 25. Examples of Newton’s 1st Law of Motion
- 26. Examples of Newton’s 1st Law of Motion
- 27. Write about it! Write down one example of inertia you see in the room.
- 28. Bell Work What is Newton’s 1st Law of Motion? Is an example of Newton’s 1st Law when a car turns left and you appear to slide to the right? What is inertia?
- 29. 2nd Law
- 30. What does F = ma say? F = ma basically means that the force of an object comes from its mass and its acceleration. Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force. Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.
- 31. Newton’s Second Law of Motion The acceleration of an object depends on the mass of the object and the amount of the force applied
- 32. Newton’s Second Law of Motion 1. Force = mass x acceleration F=m x a 2. Force- a push or pull, all forces have size and direction 3. Mass- the amount of matter an object is made of 4. Acceleration-the rate at which velocity changes; and object accelerates if its speed changes, if its direction changes and if both speed and direction changes
- 33. Newton’s Second Law of Motion
- 34. Newton’s Second Law of Motion Sample Problem Suppose a ball of mass 0.60 kg was hit with a force of 12 N. What is its acceleration? Solution: a=F/m a=12N/0.60kg a= 20 m/s2 System of Units Force Mass Acceleration SI (mks) Newton (N) Kg m/s2 SI (cgs) Dyne G cm/s2 English Pound (lb) slug ft/s2
- 35. Newton’s Second Law of Motion 2. If the force was increased to 24 N for the same ball, what is its acceleration? Solution: a=F/m a=24N/0.60kg a= 40 m/s2
- 36. Examples of Newton’s 2nd Law 1. Hitting a softball, the harder the hit, the faster the ball goes 2. Football players and their positions 3. Loaded versus an unloaded truck
- 37. Examples of Newton’s 2nd Law
- 38. Examples of Newton’s 2nd Law
- 40. Bell Work • What is Newton’s 2nd Law of Motion? • What is an example of Newton’s 2nd Law? • What is friction?
- 42. 3rd Law For every action, there is an equal and opposite reaction. Law of Interaction
- 44. Newton’s Third Law of Motion 1. For every force, there is an equal and opposite force 2. Action and Reaction
- 45. Examples of Newton’s 3rd Law 1. 2 cars hit head on 2. Jumping out of a boat onto a dock 3. Astronauts in space
- 46. 3rd Law According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
- 47. 3rd Law There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.
- 48. Newton’s 3rd Law in Nature Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).
- 49. 3rd Law Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.
- 50. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). Action-reaction force pairs make it possible for birds to fly.
- 68. MASS AND WEIGHT The difference between mass and weight is one of the most frequently asked questions. Some students often use the terms mass and weight interchangeably, which is completely wrong.
- 69. MASS AND WEIGHT
- 70. Comparison and differences between mass and weight Definition Mass is simply the measurement of the amount of matter in a body. Definition Weight is the measurement of the amount of force acting on a mass due to acceleration due to gravity.
- 71. Comparison and differences between mass and weight Denotation Mass is denoted by “M.” The SI unit of mass is Kilogram (Kg). Denotation Weight is denoted by “W.” The SI unit of weight is Newton (N).
- 72. Comparison and differences between mass and weight Gravitational Mass does not depend upon gravity and is constant everywhere. Mass can never be zero. Gravitational Weight is dependent on gravity, and so, it varies from place to place. Weight can be zero where there is no gravity (like space).
- 73. Comparison and differences between mass and weight Measuring Instrument Mass can be easily measured using any ordinary balance like beam balance, lever balance, pan balance, etc. Measuring Instrument Weight can be measured by a spring balance or by using its formula.