Ch 2 Linear Motion

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Ch 2 Linear Motion

  1. 1. Ch 2 Linear Motion Motion in a straight line
  2. 2. All Motion is Relative! <ul><li>… ..even as we sit still, we are hurdling through space. </li></ul><ul><li>When we describe motion we do it with regards to something. </li></ul><ul><li>The Train is leaving the station or is the station leaving the </li></ul><ul><li>train? </li></ul><ul><li>• A car in the Indy 500 travels 500 miles in the race but ends up </li></ul><ul><li>at the same point. </li></ul><ul><li>• On the school bus traveling at 30mph you throw a ball to a </li></ul><ul><li>classmate, how fast is the ball moving? </li></ul><ul><li>• We usually describe motion relative to the surface of the Earth. </li></ul>
  3. 3. Speed <ul><li>• Speed is a “scalar quantity” – this means it does not include direction. </li></ul><ul><li>Speed is my distance covered divided by the time it takes me </li></ul><ul><li>I am running at 10miles per hours, but I do not tell you where – this is speed. </li></ul><ul><li>Speed = distance/time </li></ul><ul><li>– Miles per hour (mi/h), kilometers per hour (km/h), </li></ul><ul><li>meters per second (m/s), light-years per century </li></ul><ul><li>– The symbol / is read as “per” </li></ul>
  4. 4. Speed cont.. <ul><li>Speed is the measure of how fast something </li></ul><ul><li>moves, it is a unit of distance divided by a </li></ul><ul><li>unit of time. We think of it in two ways. </li></ul><ul><li>– Instantaneous speed </li></ul><ul><li>– Average Speed </li></ul><ul><li>• Instantaneous Speed: speed at any given instant. “speedometer” </li></ul><ul><li>– • Average Speed: total distance/ total time </li></ul>
  5. 5. Velocity <ul><li>Is a vector, meaning it includes direction. </li></ul><ul><li>Ex: a car travels at 60 km/hr heading north. </li></ul><ul><li>Going in a straight line at the same speed is called constant velocity . </li></ul><ul><li>But changing speed (hit the brakes) or direction ( turn a corner), then we have a change in velocity. </li></ul><ul><li>Changing velocity (in either way) is called acceleration. </li></ul>
  6. 6. Acceleration <ul><li>“how quickly velocity changes”. ( or how fast you change speeds) </li></ul><ul><li>Can be positive or negative. </li></ul><ul><li>Positive acceleration – speeding up. </li></ul><ul><li>Negative acceleration – slowing down, and is sometimes called deceleration. </li></ul><ul><li>Remember that changing directions – even at a constant speed is an acceleration. </li></ul>
  7. 7. Acceleration formula <ul><li>A= change in velocity/change in time. </li></ul><ul><li>… some ways you might see this written: </li></ul><ul><li>V f = final velocity </li></ul><ul><li>V i = initial velocity </li></ul><ul><li>∆ v = change in velocity ( subtract, final – initial) </li></ul><ul><li>a = vf – vi </li></ul><ul><li>∆ t </li></ul><ul><li>Units can vary: m/s/s, mi/hr/s, km/hr/s or m/s 2 </li></ul>
  8. 8. Directions <ul><li>Directions can be positive or negative! </li></ul><ul><li>Be careful with your signs. </li></ul><ul><li>For example: someone moving backwards or down would be moving in a negative direction. </li></ul>
  9. 9. Graphing Motion <ul><li>The slope of a graph can tell you a lot about the motion and save you some equations! </li></ul><ul><li>The slope of a distance time graph is speed ( velocity). </li></ul><ul><li>The slope of a velocity time graph is acceleration! </li></ul>
  10. 10. Graphing Examples <ul><li>http://www.broadeducation.com/htmlDemos/AbsorbPhysicsAdvd/DistanceTime/page.htm </li></ul>
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