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Chapter 10.3-10.5

Chapter 10.3-10.5. 8 th Grade. Galileo Galilei Italian Astronomer Suggested that once an object is in motion, no force is needed to keep it moving. Force Needed to change the motion of the object. http://www.3m.co.uk/intl/uk//3mstreetwiseuk/pupils-force.htm. Newton’s 1 st Law of Motion.

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Chapter 10.3-10.5

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  1. Chapter 10.3-10.5 8th Grade

  2. Galileo Galilei • Italian Astronomer • Suggested that once an object is in motion, no force is needed to keep it moving. • Force • Needed to change the motion of the object. http://www.3m.co.uk/intl/uk//3mstreetwiseuk/pupils-force.htm

  3. Newton’s 1st Law of Motion • Restates Galileo’s ideas about force and motion • An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity unless it is acted upon by an unbalanced force.

  4. Newton’s 1st Law of Motion • This means that if an object is not moving, it will not move until a force acts on it. • If an object is already moving, it will continue to move at a constant velocity until a force acts to change either its speed or direction. • Gravity and friction are unbalanced forces that often change an object’s motion.

  5. Inertia • An object moving or not moving it resists any change to its motion. • Inertia • The tendency of an object to resist a change in motion

  6. Inertia • Newton’s 1st Law • Also called the Law of Inertia • The greater mass of an object, the greater its inertia, and the greater the force needed to change its motion.

  7. Newton’s 1st Law • http://www.youtube.com/watch?v=4NQbeZ0EXZQ

  8. Newton’s 2nd Law of Motion • Acceleration • depends on the object’s MASS and the NET FORCE acting on the object. • Net force / mass • Units = Newtons (N)

  9. Newton’s 2nd Law of Motion

  10. Newton’s 2nd Law of Motion • How do you increase acceleration? • Change the FORCE! • If mass is constant, acceleration and force change in the same way. • Decrease in mass = increase in acceleration http://www.youtube.com/watch?v=44dMPz_DPu8 http://www.youtube.com/watch?v=WzvhuQ5RWJE

  11. Newton’s 3rd Law of Motion • Whenever one object exerts a force on a second object, the second object exerts a force of equal strength in the opposite direction on the first object

  12. Newton’s 3rd Law of Motion • “Action-Reaction” forces • Ex. When a dog leaps it pushes down on the ground. The reaction force of the ground pushes the dog into the air. • Do action-reaction pairs Cancel? • No! They are acting on Different objects.

  13. Momentum • “quantity of motion” • It is the characteristic of a moving object related to the mass and velocity of the object • Equation: mass x velocity • Units = kg* m/s

  14. Momentum • The more mass an object has the more momentum it has, so the harder it is to stop the object. • Ex. A car moving 20 m/s is harder to stop than a baseball moving at 20 m/s because the car has a greater mass and greater momentum.

  15. Momentum • Amount of momentum objects have is conserved when they collide. • It can be transferred from one object to another, but none is lost. • Law of conservation of momentum • The total amount of momentum of objects that interact does not change in the absence of outside forces. • Ex. Friction http://www.youtube.com/watch?v=8bTdMmNZm2M http://www.youtube.com/watch?v=Xx9kiF00rts

  16. Determining Acceleration Word Problems • 1. A speedboat pulls a 55-kg water skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration.

  17. Determining Acceleration Word Problems • 2. What is the net force on a 1,000kg object accelerating at 3m/s2?

  18. Determining Acceleration Word Problems • 3. What net force is needed to accelerate a 25 kg cart at 14 m/s2?

  19. Determining Acceleration Word Problems • 4. Find the force it would take to accelerate an 800 kg car at a rate of 5 m/s2?

  20. Determining Acceleration Word Problems • 5. What is the net force acting on a 0.15 kg hockey puck accelerating at a rate of 12 m.s2?

  21. Momentum Word Problems • Which has more momentum: a 3.0- kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s? • Momentum = Mass X Velocity • Smaller : 3.0 kg X 1.5 m/s = 4.5 kg x m/s • Larger : 4.0 kg X 0.9 m/s = 3.6 kg x m/s

  22. Momentum Word Problems • A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has a greater momentum? • Golf Ball: 0.045 kg x 16 m/s = 0.72 kg x m/s • Baseball: 0.14 kg x 7 m/s = 0.98 kg x m/s • The baseball has greater momentum

  23. Momentum Word Problems • What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s? • 0.018 kg x 15 m/s = 0.27 kg x m/s

  24. Momentum Word Problems • What is the momentum of a 920 kg car moving at a speed of 25 m/s? • 920 kg x 25 m/s = 23,000 kg x m/s

  25. Momentum Word Problems • Which has more momentum? A 250 kg dolphin swimming at 4 m/s or a 350 kg manatee swimming at 2 m/s? • Dolphin : 250 x 4 = 1,000 kg x m/s • Manatee: 350 x 2 = 700 kg x m/s • The dolphin has more momentum!

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