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When the Acceleration is g...

When the Acceleration is g. …the object is in Free Fall. Consider a 1kg rock and a 1gram feather. Which object weighs more? A. Rock B. Feather C. Neither. When the Acceleration is g. …the object is in Free Fall. Consider a 1kg rock and a 1gram feather.

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When the Acceleration is g...

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  1. When the Acceleration is g... • …the object is in Free Fall. • Consider a 1kg rock and a 1gram feather. • Which object weighs more? • A. Rock • B. Feather • C. Neither

  2. When the Acceleration is g... • …the object is in Free Fall. • Consider a 1kg rock and a 1gram feather. • On which is the gravitation force stronger? • A. Rock • B. Feather • C. Neither

  3. When the Acceleration is g... • …the object is in Free Fall. • Consider a 1kg rock and a 1gram feather. • Which object has more mass? • A. Rock • B. Feather • C. Neither

  4. Section Titles • When the Acceleration is g... • SF=ma.......mg=ma........a=g • When the Acceleration Is Less Than g... • SF=ma.......mg-R=ma........a=g-R/m • When Acceleration Is Zero... • SF=ma.......mg-R=0........a=0

  5. Chapter 5 Newton’s Third of Motion

  6. Quiet Please...

  7. Newton’s Third Law • Action-Reaction • Whenever one body exerts a force on a second body… • …the second body exerts an equal and opposite force on the first body. • Figure 5.7

  8. You push on an box sitting on the floor horizontally with a force of 15 Newtons and the box does not move. The force of friction on the box is • A) 0 Newtons • B) 15 Newtons in the direction of your push • C) 15 Newtons opposite to your push • D) less that 15 Newtons.

  9. Questions from Page 78 and 80 • We know that the Earth pulls on the moon. Does this mean that the moon also pulls on the Earth? • A. Yes • B. No

  10. Question • An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction force is the… • (a) weight of the arrow. • (b) air resistance against the bow. • (c) friction of the ground against the archer’s feet • (d) grip of the archer’s had on the bow • (e) arrow’s push against the bowstring.

  11. Question • A skydiver falls toward the earth. The attraction of the earth on the diver pulls the diver down. What is the reaction to this force? • (a) air resistance the diver encounters while falling • (b) water resistance that will soon act upward on the diver. • (c) the attraction to the planets, stars, and every particle in the universe • (d) the attraction of the diver the earth

  12. Questions from Page 78 and 80 • A high speed bus and a bug have a head-on collision. • The force of impact splatters the bug. • Is the corresponding force that the bug exerts against the windshield greater, less, or the same?

  13. quin·tes·sen·tial • 1 : the essence of a thing in its purest and most concentrated form • 2 : the most typical example or representative

  14. Questions from Page 78 and 80 • A high speed bus and a bug have a head-on collision. • The force of impact splatters the bug. • Is the corresponding force that the bug exerts against the windshield greater, less, or the same? • A. Greater • B. Less • C. Same • D. It depends on the speed of impact. • E. All of these

  15. Definitions • Vector quantity - a quantity that has both magnitude and direction • Vector - an arrow drawn to scale used to represent a vector quantity • Scalar quantity - a quantity that has magnitude but not direction

  16. Vector or Scalar? • Speed……….. • Velocity……... • Acceleration.. • Time…………. • Distance…….. • Force………… scalar vector vector scalar scalar vector

  17. Addition of Vectors • The sum of two or more vectors is called their resultant. • To find the resultant of two vectors that are at angles to each other, we use the tip-to-tail method.

  18. Motion is Relative • Suppose that an airplane is traveling North at 120 km/h relative to the air. • (a) If the wind is blowing 20 km/h toward the North, how fast will the plane travel relative to the ground? • (b) What if the wind is blowing South? • (c) East?

  19. See this question on page 85. • Consider a boat that normally travels 10km/h in still water. • If the boat travels in a river that flows also at a rate of 10km/h, what will it velocity relative to the shore when it heads directly upstream? • When it heads directly downstream? • When it heads across the river?

  20. When the Acceleration is g... • …the object is in Free Fall. • Consider a 1kg rock and a 1gram feather. • Which has a greater acceleration when dropped from rest? • A. Rock • B. Feather • C. Neither

  21. Chapter 5 Newton’s Third of Motion

  22. Projectile Motion • A projectile is any object that is projected by some means and continues in motion by it own inertia. • Projectile Drawing. • The velocity of a projectile has a horizontal and vertical component. • Each component acts independently of the other.

  23. For the vertical motion the acceleration is 9.8m/s2 downward. • For the horizontal motion there is no acceleration.

  24. Projectile Motion • The shape of a projectiles path is a parabola. • The same range is obtained from two different projection angles that add up to 90°. • Maximum range for a projectile is achieved with a projection angle of 45°.

  25. In the presence of air resistance, the trajectory of a high-speed projectile falls short of a parabolic path. • A projectile fired horizontally will hit the ground at same time as an object… • …dropped from rest if they are released at the same height. • Demo: Ball projector and dropper

  26. Example Questions • You are driving along in an open car and throw a ball straight up into the air. Neglect air resistance. • 1. Where does the ball land relative to the car? A. In Front of the Car B. In the Car C. Behind the car

  27. Example Questions • You are driving along in an open car and throw a ball straight up into the air. Neglect air resistance. • 1. Where does the ball land relative to the car? A. In Front of the Car B. In the Car C. Behind the car

  28. 2. While the ball is still in the air you step on the accelerator. Where does the ball land relative to the car? A. In Front of the Car B. In the Car C. Behind the car

  29. 3. What if you stepped on the brake instead? A. In Front of the Car B. In the Car C. Behind the car

  30. Example Questions • You drop a ball from the window of a school bus moving a 10 miles/hour. Neglect air resistance. (a) Where does the ball land relative to your hand? Answer: Directly below your hand.

  31. (b) What is the shape of the path made by the ball seen by someone outside the bus? Answer: A parabola. http://observe.phy.sfasu.edu/courses/phy101/lectures101/Movies/Snowmobile%20and%20Flare.wmv

  32. Fast-Moving Projectiles Satellites • An earth satellite is simply a projectile that falls around the earth rather that into it. • Satellites are not free from gravity.

  33. The speed of the satellite must be great enough to ensure that its falling distance matches the earth's curvature. • It takes 1 second for an object in free fall to fall 4.9 meters. • Earth's surface 'drops' a vertical distance of 4.9 meters for every 8000 meters along the Earth's surface.

  34. This means that a satellite near the Earth’s surface must travel at 8000 meters/second! • …or 18,000 miles per hour. • For example: The space shuttle orbits the Earth once every 90 minutes.

  35. End of Chapter 5

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