L2

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Conceptual Physics, Lesson 2

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L2

  1. 1. Physics L2 www.slideshare.net/DMS_physics
  2. 2. Motion is relative <ul><li>Motion = change in position of an object </li></ul><ul><li>System of Reference </li></ul>
  3. 3. Speed <ul><li>A measure of how fast something is moving (see p.12) </li></ul><ul><li>Average speed is the total distance divided by the time interval </li></ul>
  4. 4. Instantaneous speed <ul><li>A measure of how fast an object is moving at a certain time </li></ul><ul><li>speedometer </li></ul><ul><li>odometer </li></ul>
  5. 5. Over to you <ul><li>P.13 / Q.1 </li></ul><ul><li>P.13 / Q.2 </li></ul>
  6. 6. Velocity <ul><li>has speed and direction </li></ul>
  7. 7. Scalars and Vectors <ul><li>Scalars = have only one value </li></ul><ul><ul><li>Ex: time, speed, temperature </li></ul></ul><ul><li>Vectors = have two or three values (magnitude and direction) </li></ul><ul><ul><li>Ex: velocity, force, acceleration </li></ul></ul>
  8. 8. Over to you (p.14/Q) <ul><li>The speedometer of a car moving northward reads 60 km/h. It passes another car that travels southward at 60 km/h. </li></ul><ul><ul><li>Do both cars have the same speed? </li></ul></ul><ul><ul><li>Do they have the same velocity? </li></ul></ul>
  9. 9. Constant and changing velocity <ul><li>Constant velocity </li></ul><ul><ul><li>both speed and direction are constant </li></ul></ul><ul><ul><li>The motion occurs in a straight line </li></ul></ul><ul><ul><li>Uniform (linear) motion </li></ul></ul><ul><li>Changing velocity </li></ul><ul><ul><li>Either one of speed or direction are changing, or both </li></ul></ul>
  10. 10. Over to you <ul><li>Q: What controls are used to change velocity in a car? </li></ul>
  11. 11. Over to you <ul><li>A: gas pedal, brake, steering wheel </li></ul>
  12. 12. Acceleration <ul><li>Is the rate at which velocity is changing </li></ul><ul><ul><li>Acceleration is a vector </li></ul></ul>
  13. 14. Uniform Circular Motion <ul><li>Speed is constant </li></ul><ul><li>Velocity is changing </li></ul><ul><li>Acceleration points towards the center of the motion </li></ul>
  14. 15. Classwork <ul><li>Consider a car that is leaving drops of oil on the road. Show how the drops would look if </li></ul><ul><ul><li>The car is traveling at constant velocity </li></ul></ul><ul><ul><li>The car is accelerating (increasing its velocity) </li></ul></ul><ul><ul><li>The car is decelerating (reducing its velocity) </li></ul></ul>
  15. 16. Answer Constant speed (zero acceleration) Positive acceleration (accelerating) Negative acceleration (decelerating)
  16. 17. Example (p.16/Q1) <ul><ul><li>Suppose a car moving in a straight line steadily increases its speed each second, first from 35 to 40 km/h, then from 40 to 45 km/h, then from 45 to 50 km/h. What is its acceleration? </li></ul></ul><ul><ul><li>Answer: </li></ul></ul>
  17. 18. Classwork <ul><li>P.16 / Q2 </li></ul><ul><ul><li>In 5 seconds a car moving in a straight line increases its speed from 50 km/h to 65 km/h, while a truck goes from rest to 15 km/h in a straight line. Which undergoes greater acceleration? What is the acceleration of each vehicle? </li></ul></ul>
  18. 19. Homework assignment <ul><li>P. 25 / 12 </li></ul><ul><ul><li>What is the acceleration of a car moving along a straight-line path that increases its speed from 0 to 100 km/h in 10s ? </li></ul></ul>
  19. 20. Homework assignment <ul><li>P. 25 / 13 </li></ul><ul><ul><li>By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2 km/h.s? </li></ul></ul>
  20. 21. End L2

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