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• ### L3

1. 1. Physics L3 www.slideshare.net/DMS_physics
2. 2. Free Fall <ul><li>… occurs if the only force on an object is gravity. </li></ul><ul><li>Acceleration of gravity </li></ul>For convenience we can use g = 10 m/s 2
3. 3. How Fast ? 10t t . . . . 50 5 40 4 30 3 20 2 10 1 0 0 Instantaneous Speed (m/s) Elapsed Time (s)
4. 4. How Fast ?
5. 5. Question <ul><li>What would the speed of the apple be </li></ul><ul><ul><li>after 4.5s? </li></ul></ul><ul><ul><li>after 8s? </li></ul></ul><ul><ul><li>after 15s? </li></ul></ul>10t t . . . . 50 5 40 4 30 3 20 2 10 1 0 0 Instantaneous Speed (m/s ) Elapsed Time (s)
6. 6. Speed Graph <ul><li>In Uniform Motion </li></ul><ul><ul><li>speed is directly proportional to time </li></ul></ul><ul><ul><li>The graph is a straight line </li></ul></ul><ul><ul><li>The slope is acceleration </li></ul></ul>
7. 7. Question <ul><li>What would the speed of the apple be </li></ul><ul><ul><li>after 4.5s? </li></ul></ul><ul><ul><li>after 8s? </li></ul></ul><ul><ul><li>after 15s? </li></ul></ul><ul><li>45 m/s </li></ul><ul><li>80 m/s </li></ul><ul><li>150 m/s </li></ul>
8. 8. <ul><li>Acceleration is 10m/s 2 downwards at all times </li></ul><ul><li>At the same height </li></ul><ul><ul><li>Speeds are the same </li></ul></ul><ul><ul><li>Velocities are in the opposite directions </li></ul></ul>t = 3s, v = 0m/s t = 2s t = 1s t = 0s t = 4s t = 5s t= 6s t = 7s v = 20m/s v = 10m/s v = 30m/s v = 40m/s
9. 9. t = 3s, v = 0m/s t = 2s t = 1s t = 0s t = 4s t = 5s t= 6s t = 7s v = 20m/s v = 10m/s v = 30m/s v = 40m/s
10. 10. t = 3s, v = 0m/s t = 2s t = 1s t = 0s t = 4s t = 5s t= 6s t = 7s v = 20m/s v = 10m/s v = 30m/s v = 40m/s
11. 11. Average Speed <ul><li>For objects moving with constant acceleration , the average speed is the arithmetic mean (average) of the initial and final speeds. </li></ul>10t t . . . . 50 5 40 4 30 3 20 2 10 1 0 0 Instantaneous Speed (m/s ) Elapsed Time (s)
12. 12. How far ?
13. 13. How far ? 5t 2 t . . . . 125 5 80 4 45 3 20 2 5 1 0 0 Distance (m) Elapsed Time (s)
14. 14. Classwork (p.20/Q) <ul><li>An apple falls from a tree and hits the ground in one second. </li></ul><ul><ul><li>What is its speed upon striking the ground? </li></ul></ul><ul><ul><li>What is its average speed during this 1s? </li></ul></ul><ul><ul><li>How high above the ground was the apple when it was dropped? </li></ul></ul>
15. 16. Homework Assignment <ul><li>P.26 / 16,17,19 </li></ul><ul><ul><li>For a freely falling object dropped from rest, what is the </li></ul></ul><ul><ul><ul><li>Instantaneous speed at the end of the fifth second of fall? </li></ul></ul></ul><ul><ul><ul><li>Acceleration at the end of the fifth second of fall? </li></ul></ul></ul><ul><ul><ul><li>Distance covered by the end of the fifth second of fall? </li></ul></ul></ul>
16. 17. End L3 www.slideshare.net/DMS_physics