Ppt Air Resistance

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Ppt Air Resistance

  1. 1. Air Resistance
  2. 2. Air Resistance <ul><li>What two forces are acting on an object when it falls? </li></ul><ul><li>F g </li></ul><ul><li>Air resistance </li></ul>
  3. 3. Air Resistance <ul><li>Imagine dropping two pieces of paper. One is crumpled and the other is flat. </li></ul><ul><li>Which one will reach the ground faster and why? </li></ul><ul><li>The crumpled one because it has less surface area. Dr. Fiala demonstrated this in class! </li></ul>
  4. 4. Air Resistance <ul><li>When something falls, air resistance acts in the opposite direction as the force of gravity. </li></ul><ul><li>Air resistance acts in the opposite direction of the object’s motion. y </li></ul><ul><li>F a </li></ul><ul><li>x </li></ul><ul><li>F g </li></ul>
  5. 5. Air Resistance <ul><li>The amount of air resistance an object experiences depends on three things: </li></ul><ul><li>Speed </li></ul><ul><li>Size </li></ul><ul><li>Shape </li></ul>
  6. 6. Air Resistance <ul><li>Why do leaves, papers, feathers fall at different speeds than acorns, pens, and glasses? </li></ul><ul><li>Because of Air Resistance… </li></ul><ul><li>Air resistance not mass is responsible for the difference in objects falling speed. </li></ul>
  7. 7. Terminal Velocity <ul><li>As an object falls, it accelerates and its speed increases until the force of air resistance, which is increasing with speed, becomes equal and opposite the force of gravity. </li></ul>
  8. 8. Terminal Velocity <ul><li>The force of air resistance increases until it becomes large enough to be equal and opposite the force of gravity which results in a net force of zero. </li></ul><ul><li>According to Newton’s 2 nd law, F = ma. So if the net force is zero, the object can no longer be accelerating. </li></ul><ul><li>The object then falls at a constant speed called terminal velocity. </li></ul>
  9. 9. Terminal Velocity <ul><li>Terminal Velocity is the highest velocity that a falling object will reach. </li></ul><ul><li>A low terminal velocity allows the skydiver to land safely. </li></ul>
  10. 10. Terminal Velocity <ul><li>Why would a skydiver want to lay out flat versus falling standing up? </li></ul><ul><li>Think about our paper example… crumpled vs. flat </li></ul>

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