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Chapter 8 Motion

Chapter 8 Motion. 1. Speed 2. Vectors 3. Acceleration 4. Distance, Time, and Acceleration 5. Free Fall System 6. Air Resistance 7. First Law of Motion. 8. Mass 9. Second Law of Motion 10. Mass and Weight 11. Third Law of Motion 12. Circular Motion 13. Newton's Law of Gravity

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Chapter 8 Motion

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  1. Chapter 8 Motion 1. Speed 2. Vectors 3. Acceleration 4. Distance, Time, and Acceleration 5. Free Fall System6. Air Resistance7. First Law of Motion 8. Mass 9. Second Law of Motion 10. Mass and Weight 11. Third Law of Motion 12. Circular Motion 13. Newton's Law of Gravity 14. Artificial Satellites

  2. 1. Speed • Definitions: • Speed • The rate at which something moves a given distance. • Faster speeds = greater distances • General formula for speed: • Speed = distance / time • Abbreviations commonly used: • d = distance t = time v = speed • v = d/t

  3. 1. Speed Velocity Distance Time

  4. 1. Speed Average speed is the total distance traveled by an object divided by the time taken to travel that distance.  Instantaneous speed is an object's speed at a given instant of time.

  5. 2. Vectors Magnitude of a quantity tells how large the quantity is. Scalar quantities have magnitude only. Vector quantities have both magnitude and direction.

  6. 2. Vectors Velocity is a vector quantity that includes both speed and direction.

  7. Velocity Example You are watching someone split wood with a sledge hammer & a wedge. When watching, you notice that it takes 3 seconds for you to hear the sound after you see the sledge strike the wedge. Given that sound travels at 330 m/s at that temperature, find the distance from the wood splitter to you.

  8. 3. Acceleration Acceleration of an object is the rate of change of its velocity and is a vector quantity. For straight-line motion, average acceleration is the rate of change of speed:

  9. 2-3. Acceleration 3 Types of Acceleartion Speeding Up Slowing Down Turning

  10. 2- 4. Distance, Time and Acceleration (V1 + V2) Vavg = 2 (20mph + 60mph) = 40mph 2 d = vavg t d = ½at2 30mph 2hr = 60miles ½ 10m/s/s 52 = 125m

  11. 2-5. Free Fall The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2. Galileo found that all things fall at the same rate.

  12. 2-5. Free Fall The rate of falling increases by 9.8 m/s every second. Height = ½ gt2 For example: ½ (9.8 )12 = 4.9 m½(9.8)22 = 19.6 m ½ (9.8)32 = 44.1 m ½ (9.8)42 = 78.4 m

  13. 2-5. Free Fall A ball thrown horizontally will fall at the same rate as a ball dropped directly.

  14. 2-5. Free Fall A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity. When it passes the thrower, it will be traveling at the same rate at which it was thrown.

  15. 2-5. Free Fall An object thrown upward at an angle to the ground follows a curved path called a parabola.

  16. 2-6. Air Resistance • In air… • A stone falls faster than a feather • Air resistance affects stone less • In a vacuum • A stone and a feather will fall at the same speed.

  17. 2-6. Air Resistance • Free Fall • A person in free fall reaches a terminal velocity of around 54 m/s • With a parachute, terminal velocity is only 6.3 m/s • Allows a safe landing

  18. 2-6. Air Resistance • Ideal angle for a projectile • In a vacuum, maximum distance is at an angle of 45o • With air resistance (real world), angle is less • Baseball will go furthest hit at an angle of around 40o

  19. 2-7. First Law of Motion The first law of motion states: If no net force acts on it, an object at rest remains at rest and an object in motion remains in motion at a constant velocity.

  20. Foucault Pendulum Inertia keeps a pendulum swinging in the same direction regardless of the motion of the earth. This can be used to measure the motion of the earth. As the Foucault Pendulum swings it appears to be rotating, but it is the earth that is rotating under it. To the right is the Foucault Pendulum at the Pantheon in Paris, France.

  21. Foucault Pendulum Other Web sites that illustrate the Foucault Pendulum. http://en.wikipedia.org/wiki/File:Foucault-rotz.gif http://www.physclips.unsw.edu.au/jw/foucault_pendulum.html http://aspire.cosmic-ray.org/labs/scientific_method/pendulum.swf http://www.calacademy.org/products/pendulum/page7.htm http://www.youtube.com/watch?v=nB2SXLYwKkM

  22. 2-8. Mass Inertia is the apparent resistance an object offers to any change in its state of rest or motion.

  23. 2-9. Second Law of Motion Newton's second law of motion states: The net force on an object equals the product of the mass and the acceleration of the object. The direction of the force is the same as that of the acceleration. F = Ma

  24. 2-9. Second Law of Motion A force is any influence that can cause an object to be accelerated. The pound (lb) is the unit of force in the British system of measurement: 1 lb = 4.45 N (1 N = 0.225 lb)

  25. 2-10. Mass and Weight • Weight • Definition: The force with which an object is attracted by the earth’s gravitational pull • Example: A person weighing 160 lbs is being pulled towards the earth with a force of 160 lbs (712 N). • Near the earth’s surface, weight and mass are essentially the same

  26. 2-11. Third Law of Motion The third law of motion states: When one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.

  27. 2-11. Third Law of Motion Examples of the 3rd Law

  28. 2-12. Circular Motion Centripetal force is the inward force exerted on an object to keep it moving in a curved path. Centrifugal force is the outward force exerted on the object that makes it want to fly off into space.

  29. 2-12. Circular Motion

  30. 2-12. Circular Motion 833 N is needed to make this turn. If he goes too fast, which wheels are likely to come off the ground first?

  31. 2-13. Newton's Law of Gravity G = 6.67 x 10-11 N•m/kg2

  32. 2-13. Newton's Law of Gravity • How can we determine the mass of the earth using an apple? • This illustrates the way scientists can use indirect methods to perform seemingly “impossible tasks”

  33. 2-13. Newton's Law of Gravity • How can we determine the mass of the earth using an apple? • This illustrates the way scientists can use indirect methods to perform seemingly “impossible tasks” = mg

  34. 2-15. Artificial Satellites • The world's first artificial satellite was Sputnik I, launched in 1957 by the Soviet Union. GPS-Global Positioning Satellite

  35. 2-15. Artificial Satellites The escape speed is the speed required by an object to leave the gravitational influence of an astronomical body; for earth this speed is about 40,000 km/h.

  36. 2-15. Artificial Satellites The escape speed is the speed required by an object to leave the gravitational influence of an astronomical body; for earth this speed is about 40,000 km/h.

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