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Newton's Laws

Newton's Laws. Summary of Discussion:. Newton’s First Law inertia Mass vs. Weight Newton’s Second Law F=ma a=f/a Newton’s Third Law. Inertia. INERTIA. The tendency of objects to remain in motion or stay at rest

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Newton's Laws

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  1. Newton's Laws

  2. Summary of Discussion: • Newton’s First Law • inertia • Mass vs. Weight • Newton’s Second Law • F=ma • a=f/a • Newton’s Third Law

  3. Inertia INERTIA • The tendency of objects to remain in motion or stay at rest • If it were not for friction, an object set in motion would continue to move forever

  4. Newton’s First Law FIRST LAW OF MOTION • An object at rest remains at rest, or if in a state of motion, continues at constant velocity (same direction & speed) unless acted upon by an outside force

  5. Inertia Riding In A Car . . . • When you are riding in a car and it stops suddenly, you keep moving forward • if you did not have a safety belt to stop you, your inertia could send you through the windshield

  6. Inertia Standing On A Bus . . . • When the bus starts to move forward you are thrown off balance and fall backward • Your body has inertia • it is at rest and tends to stay at rest, even though the bus is moving

  7. Inertia . . . On The Same Bus • When the moving bus stops, you fall forward • Even though the bus stops, you do not • You are an object in motion

  8. Mass vs. Weight MASS VS. WEIGHT • Weight • a measure of the force of gravity on an object • weight = mass x acceleration due to gravity w = m x g • measured in Newtons • Mass • a constant value; does not change • amount of matter • measured in Kilograms

  9. Weight CALCULATING WEIGHT • measured in Newtons • weight = mass x acceleration due to gravity w = m x g • acceleration due to gravity on Earth = 9.8 N/kg • Example: m = 100 kg g = 9.8 N/kg • Weight =100 kg x 9.8 N/kg = 980 N

  10. Weight WEIGHT • Varies according to the force of gravity pulling on you • a smaller mass means a smaller gravitational pull Where would you weigh more? Why? Earth Moon

  11. Mass MASS • Remains constant • You have the same amount of mass regardless of your location Would your mass change? Why or why not? Earth Moon

  12. Newton’s Second Law NEWTON’S SECOND LAW • A force acting on an object will produce an acceleration of the object proportional to the force and in the direction of the applied force • if you double the force that you throw a ball, you willdouble its acceleration

  13. Newton’s Second Law Mathematically Speaking... • Force = mass x accelerationF = ma

  14. Newton’s Second Law F = ma • If the same force is applied to a bowling ball and a tennis ball, which ball will have the greateracceleration? WHY?

  15. Remember: F = ma Newton’s Second Law Force Measured in Newtons • 1 N = 1 kg x 1 m/sec/sec = kg m s2 • One newton equals the force required to accelerate one kilogram of mass at one meter/second/second

  16. Small Car mass = 750 kg acceleration = 2 m/sec/sec Force required to accelerate car = 750 kg x 2 m/sec/sec = 1500 N Large Car mass = 1000kg acceleration = 2 m/sec/sec Force required to accelerate car = 1000 kg x 2 m/sec/sec = 2000 N Remember: F = ma Newton’s Second Law Better Gas Mileage?

  17. Newton’s Second Law Not Just: F = ma • Formula can also be written as:a = F/m • Acceleration is directly proportional to the force • Acceleration is indirectly proportional to the mass

  18. Acceleration REMEMBER: • Acceleration does not only mean to go faster! • Acceleration can mean: • direction of motion changed • motion started • motion stopped • speed increased • speed decreased

  19. decreases remains constant a = F m increases Acceleration a = F/m • If a person keeps adding snow to the snowball (increasing its mass), yet each time throws it with the same force, the snowball will accelerate less each time

  20. increases remains constant a = F m decreases Acceleration a = F/m • If the snowball begins to melt (mass decreases), the same force applied to the snowball will cause it to accelerate more

  21. Newton’s Third Law NEWTON’S THIRD LAW • For every action, there is an equal and opposite reaction • Every force must have an equal and opposite force • all forces come in pairs

  22. Equal and opposite forces Newton’s Third Law EQUAL AND OPPOSITE FORCES • You move forward and the earth moves in the opposite direction! • Since the mass of the earth is so large, its motion is unobservable • As you walk, your feet push against the ground • The ground pushes up against your feet with an equal and opposite force

  23. Equal and opposite forces Newton’s Third Law Space Shuttle • Various fuels are burned in the engine, producing hot gases • As the gases move downward, the rocket moves in the opposite direction, or upward

  24. TOPICS COVERED: • Newton’s First Law • inertia • Mass vs. Weight • Newton’s Second Law • F=ma • a=f/a • Newton’s Third Law

  25. Bibliography • K. Batista notes • Physical Science (1988). HBJ, pp.313-316; pp.322-323

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