newtons_laws_of_motion presentation .ppt
- 1. Newton’s Newton’s Laws of Laws of Motion Motion I. I. Law of Inertia Law of Inertia II. II. F=ma F=ma III. III. Action-Reaction Action-Reaction
- 2. While most people know While most people know what Newton's laws say, what Newton's laws say, many people do not know many people do not know what they mean (or simply do what they mean (or simply do not believe what they mean). not believe what they mean).
- 3. Newton’s Laws of Motion Newton’s Laws of Motion 1 1st st Law Law – An object at rest will stay at rest, – An object at rest will stay at rest, and an object in motion will stay in and an object in motion will stay in motion at constant velocity, unless acted motion at constant velocity, unless acted upon by an unbalanced force. upon by an unbalanced force. 2 2nd nd Law Law – – Force equals mass times Force equals mass times acceleration. acceleration. 3 3rd rd Law Law – – For every action there is an For every action there is an equal and opposite reaction. equal and opposite reaction.
- 4. 1 1st st Law of Motion Law of Motion (Law of Inertia) (Law of Inertia) An object at rest will stay at An object at rest will stay at rest, and an object in motion rest, and an object in motion will stay in motion at will stay in motion at constant velocity, unless acted constant velocity, unless acted upon by an unbalanced force. upon by an unbalanced force.
- 5. 1 1st st Law Law Inertia is the Inertia is the tendency of an tendency of an object to resist object to resist changes in its changes in its velocity: velocity: whether in whether in motion or motion or motionless. motionless. These pumpkins will not move unless acted on by an unbalanced force.
- 6. 1 1st st Law Law Once airborne, Once airborne, unless acted on unless acted on by an by an unbalanced force unbalanced force (gravity and air (gravity and air – fluid friction), – fluid friction), it would never it would never stop! stop!
- 7. 1 1st st Law Law Unless acted Unless acted upon by an upon by an unbalanced unbalanced force, this golf force, this golf ball would sit on ball would sit on the tee forever. the tee forever.
- 8. Why then, do we observe Why then, do we observe every day objects in motion every day objects in motion slowing down and becoming slowing down and becoming motionless seemingly without an motionless seemingly without an outside force? outside force? It’s a force we sometimes cannot see – It’s a force we sometimes cannot see – friction. friction.
- 9. Objects on earth, unlike the Objects on earth, unlike the frictionless space the moon frictionless space the moon travels through, are under the travels 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 an object in motion? What is this unbalanced force that acts on an object in motion?
- 11. Slide a book Slide a book across a table and across a table and watch it slide to a rest watch it slide to a rest position. The book position. The book comes to a rest comes to a rest because of the because of the presence presence of a force - of a force - that force being the that force being the force of friction - force of friction - which brings the book which brings the book to a rest position. to a rest position.
- 12. In the absence of a force of friction, the book In the absence of a force of friction, the book would continue in motion with the same speed would continue in motion with the same speed and direction - forever! (Or at least to the end and direction - forever! (Or at least to the end of the table top.) of the table top.)
- 13. Newtons’s 1 Newtons’s 1st st Law and You Law 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) resist changes Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour. by the brick wall, your body keeps moving at 80 m/hour.
- 14. 2 2nd nd Law Law
- 15. 2 2nd nd Law Law The net force of an object is The net force of an object is equal to the product of its mass equal to the product of its mass and acceleration, or F=ma. and acceleration, or F=ma.
- 16. 2 2nd nd Law Law When mass is in kilograms and acceleration is When 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 to One newton is equal to the force required to accelerate one kilogram of mass at one accelerate one kilogram of mass at one meter/second/second. meter/second/second.
- 17. 2 2nd nd 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 formula Write the formula F = m x a Fill in given numbers and units Fill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknown Solve for the unknown 2800 kg-meters/second/second or 2800 N
- 18. If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.
- 19. 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 = ma F = ma 98 N = 10 kg x 9.8 m/s/s 98 N = 10 kg x 9.8 m/s/s F = ma F = ma 9.8 N = 1 kg x 9.8 9.8 N = 1 kg x 9.8 m/s/s m/s/s
- 21. Check Your Understanding Check Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg 1. What acceleration will result when a 12 N net force applied to a 3 kg object? 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/s 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2 2 . . 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 9.8 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? m/sec/sec?
- 22. Check Your Understanding Check 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/s 12 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/s 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2 2 . Determine the . Determine the mass. mass. 16 N = 3.2 kg x 5 m/s/s 16 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 N 66 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 N 9800 kg-m/sec/sec or 9800 N
- 24. 3 3rd rd Law Law For every action, there is an For every action, there is an equal and opposite reaction. equal and opposite reaction.
- 25. 3 3rd rd Law Law According to Newton, According to Newton, whenever objects A and whenever objects A and B interact with each B interact with each other, they exert forces other, they exert forces upon each other. When upon each other. When you sit in your chair, you sit in your chair, your body exerts a your body exerts a downward force on the downward force on the chair and the chair chair and the chair exerts an upward force exerts an upward force on your body. on your body.
- 26. 3 3rd rd Law Law There are two forces There are two forces resulting from this resulting from this interaction - a force on interaction - a force on the chair and a force on the chair and a force on your body. These two your body. These two forces are called forces are called action action and and reaction reaction forces. forces.
- 27. Newton’s 3rd Law in Nature Newton’s 3rd Law in Nature Consider the propulsion of a Consider the propulsion of a fish through the water. A fish fish through the water. A fish uses its fins to push water uses its fins to push water backwards. In turn, the water backwards. In turn, the water reacts reacts by pushing the fish by pushing the fish forwards, propelling the fish forwards, propelling the fish through the water. through the water. The size of the force on the The size of the force on the water equals the size of the water equals the size of the force on the fish; the direction force on the fish; the direction of the force on the water of the force on the water (backwards) is opposite the (backwards) is opposite the direction of the force on the direction of the force on the fish (forwards). fish (forwards).
- 28. 3 3rd rd Law Law Flying gracefully Flying gracefully through the air, birds through the air, birds depend on Newton’s depend on Newton’s third law of motion. As third law of motion. As the birds push down on the birds push down on the air with their wings, the air with their wings, the air pushes their the air pushes their wings up and gives wings up and gives them lift. them lift.
- 29. Consider the flying motion of birds. A bird flies by Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird downwards. In turn, the air reacts by pushing the bird upwards. upwards. The size of the force on the air equals the size of the 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 force 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 on the bird (upwards). the bird (upwards). Action-reaction force pairs make it possible for birds Action-reaction force pairs make it possible for birds to fly. to fly.
- 31. Other examples of Newton’s Other examples of Newton’s Third Law Third Law The baseball forces the The baseball forces the bat to the left (an bat to the left (an action); the bat forces action); the bat forces the ball to the right (the the ball to the right (the reaction). reaction).
- 32. 3 3rd rd Law Law Consider the motion of Consider the motion of a car on the way to a car on the way to school. A car is school. A car is equipped with wheels equipped with wheels which spin backwards. which spin backwards. As the wheels spin As the wheels spin backwards, they grip the backwards, they grip the road and push the road road and push the road backwards. backwards.
- 33. 3 3rd rd Law Law The reaction of a rocket is The reaction of a rocket is an application of the third an application of the third law of motion. Various law of motion. Various fuels are burned in the fuels are burned in the engine, producing hot engine, producing hot gases. gases. The hot gases push against The hot gases push against the inside tube of the rocket the inside tube of the rocket and escape out the bottom and escape out the bottom of the tube. As the gases of the tube. As the gases move downward, the rocket move downward, the rocket moves in the opposite moves in the opposite direction. direction.