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  1. 1. Notes: Gravity S: Gravity and Acceleration
  2. 2. Gravity March 6, 2009
  3. 3. Aristotle <ul><li>Ancient Greece around 400 BC </li></ul><ul><li>He believed that the heavier the object, the faster it falls. </li></ul>
  4. 4. <ul><li>In the late 1500s, an Italian scientist named Galileo Galilei decided to prove Aristotle wrong. </li></ul><ul><li>Galileo theorized that all objects will land at the same time when they are dropped from the same height . </li></ul>
  5. 6. Elephants & feathers <ul><li>Objects fall to the ground at the same rate because acceleration due to gravity is the same for all objects. </li></ul>
  6. 7. What is gravity? Galileo helped us understand gravity as a force that exists between the Earth and objects. Newton showed that the same force exists between all objects. Even today, no one knows exactly why objects attract each other.
  7. 8. It all starts with an apple… <ul><li>Isaac Newton 1655 </li></ul>
  8. 9. <ul><li>The size of the gravitational force depends on two things: </li></ul><ul><ul><li>Mass of the objects </li></ul></ul><ul><ul><li>Distance between the objects </li></ul></ul>The Law of Universal Gravitation
  9. 10. What is weight? <ul><li>Weight is a measure of the gravitational force exerted on an object. </li></ul><ul><li>Since gravity is a force and weight is a measure of gravity, weight is expressed in newtons (N). </li></ul>
  10. 11. Gravity & Acceleration <ul><li>The rate at which objects accelerate towards Earth is </li></ul><ul><li>9.8 m/s 2 . </li></ul><ul><li>It is the same for all objects, regardless of their mass. </li></ul>
  11. 12. Air Resistance <ul><li>The amount of air resistance depends on the size and shape of an object. </li></ul><ul><li>While gravity pulls an object down, towards the Earth, the air resistance pushes an object up, or away from the Earth. </li></ul>
  12. 13. Free Fall <ul><li>When there is no air resistance, an object is in free fall. </li></ul><ul><li>An object is in free fall only if gravity is pulling it down and no other forces are acting on it. </li></ul>
  13. 15. Terminal Velocity <ul><li>Force of gravity = air resistance </li></ul><ul><li>This is the highest velocity reached by a falling object thus it has 0 acceleration and falls with constant velocity. </li></ul>