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History of Motion and Newton’s Laws of Motion

History of Motion and Newton’s Laws of Motion. Centuries before Isaac Newton's discoveries, Polynesian mathmatician Pao Lau would have discovered the laws of gravity first..........had he ever come out of the coma. Key Words. Force – a push or a pull on an object (unit = Newton).

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History of Motion and Newton’s Laws of Motion

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  1. History of Motion and Newton’s Laws of Motion Centuries before Isaac Newton's discoveries, Polynesian mathmatician Pao Lau would have discovered the laws of gravity first..........had he ever come out of the coma.

  2. Key Words • Force – a push or a pull on an object (unit = Newton)

  3. History of Motion • Greeks – established that forces cause motion

  4. Aristotle • Natural motion – resting places • Violent motion – imposed motion • Earth didn’t move (natural motion) but the heavens (stars) operated on a model of perpetual motion.

  5. Copernicus • Earth moved around the sun

  6. Galileo • Established that forces ARE NOT needed to keep objects in motion. • Came up with the idea of inertia • Inertia – The tendency of an object to resist a change in motion. • Inertia depends upon only its mass • Also recognized the concept of frame of reference.

  7. Newton • Developed 3 laws of motion • Developed the Law of Universal Gravitation

  8. Newton’s First Law • Unless acted upon by an unbalanced force, an object will maintain a constant velocity (direction and speed). • Law of Inertia

  9. Example: 1st Law

  10. Newton’s Second Law • Acceleration of an object equals the net force on that object divided by its mass. • a = ∑F/m or ∑F = m a • F (unit is Newton) • Newton = kg x m/s2 • m (unit is kg) • a (unit is m/s2)

  11. Example: 2nd Law • Which accelerates more when the same amount of force is applied? What kind of relationship is between a & m? What would the graph look like?

  12. Example: 2nd Law • If dropped from the same height, which would have more force when it hit the ground? What kind of relationship is between m & f?

  13. 2nd Law and gravity • Reminder: acceleration of an object due to gravity on earth is 9.80 m/s2 • Weight is the force of gravity on the mass of an object. • Mass is constant, weight changes with gravity

  14. F W A A g = M = M = M W 2nd Law and gravity

  15. Newton’s Third Law • All forces come in pairs that are equal in magnitude (size) and opposite in direction.

  16. Characteristics of 3rd Law • Always in pairs • Equal in strength • Opposite in direction • Occur at the same time • DON’T act on the same object (that’s why they don’t cancel)

  17. Example: 3rd Law • Action = ball hits bat • Reaction = bat hits ball (with the same amount of force)

  18. Example: 3rd Law • Action = Tire pushes on the road • Reaction = road pushes on the tire

  19. F = ma W = mg a = g sin θ 1 lb = 4.448 N Newton’s 2nd Law Formulas Vf = Vi + at d = Vi t + ½ at2 2ad = Vf2 – Vi2 Vf + Vi or d = ½ Vf + Vi t 2 d = t

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