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Motion

Motion. Speed, acceleration, momentum. Frames of Reference. Object or point from which motion is determined Most common is the earth Motion is a change in position relative to a frame of reference. What is motion?.

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Motion

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  1. Motion Speed, acceleration, momentum

  2. Frames of Reference • Object or point from which motion is determined • Most common is the earth • Motion is a change in positionrelative to a frame of reference

  3. What is motion? • If you are standing in one place, and your friend walks by you, are you moving relative to your friend? • Is your friend moving relative to you? • Is either of you moving relative to the earth?

  4. Answer: • You are moving relative to your friend, and your friend is moving relative to you! • You (the Joker) are not moving relative to the earth, but your friend is. You are both moving relative to the sun! Who is moving relative to the computer screen?

  5. What is motion? • If you and your friend are walking down the hall together at the same speed, in the same direction, are you moving relative to your friend? • Is your friend moving relative to you? • Are either of you moving relative to the earth?

  6. Answer: • You are NOT moving relative to your friend, and your friend is NOT moving relative to you. You both are moving relative to the earth.

  7. Speed • Speed = Distance ÷ Time D_ S T Example: A car travels 300km in 6 hours. What is the speed of the car?

  8. Answer: • Speed = distance ÷ time • Speed = 300km ÷ 6 hours • Speed = 50km/hr

  9. More practice • 1. How far can a plane travel if it flies 800km/hr for 9 hours? • 2. How long does it take a ship to go 500 km if it travels at a speed of 50km/hr?

  10. Answer 1. D S T D 800 9 800km ▪ 9hrs = 7200km hr

  11. Answer 2. D S T 500 50 T 500km ÷ 50km = 10 hrs hr

  12. Velocity • Speed in a given direction. • What is the velocity of a boat that travels from St. Peter to Mankato (10 miles) in 15 minutes?

  13. Answer • Speed = distance ÷ time • Speed = 10 miles ÷ 15 minutes • Speed = 0.67 mi/min • Velocity = 0.67 mi/min South

  14. Change your answer to mi/hr! • 0.67mi/min x 60min/hr = • 40 mi/hr

  15. Distance-time graphs • On your paper, graph the following: • D (m) T (sec) 0 0 5 7 10 14 15 21

  16. Distance (m) time (sec)

  17. Was your graph a straight line? • A distance-time graph which is a straight line indicates constant speed. • In constant speed, the object does not speed up or slow down. The acceleration is zero.

  18. Graph the following on a distance-time graph: • D (m) T (s) 0 0 5 1 20 2 45 3 80 4 125 5

  19. Distance (m) 0 1 2 3 4 5 time (sec)

  20. Was your graph a curve? • A graph that curves on a distance-time graph shows that the object is accelerating

  21. Distance-time graphs • Describe the motion of the object as shown in the graph. From 0-8 sec, constant speed: (25 m/sec); From 8-12 sec, no motion; From 12-16 sec, acceleration; From 16-20 sec, constant speed

  22. Speed-time graphs • Using the distance-time graph from the last frame, draw a speed time graph. First fill in the table below: Average Speed (m/s) Time (sec) ____ 0 to 8 ____ 8 to 12 ____ 12 to 20 25 0 37.5

  23. What does your graph look like? • Constant speed will be a horizontal line on a speed time graph. • If the speed decreases, the line will slant down. • If the speed increases, the line will slant up.

  24. What do the following speed-time graphs depict?

  25. Acceleration • Change in velocity • Can be change in speed or direction • Acceleration = Vi – Vf t

  26. Acceleration problem • A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?

  27. Answer • Acceleration = ∆V/ ∆T • a = 26m/s – 10m/s 2 s a = 16m/s 2s a = 8m/s/s or 8m/s2

  28. More acceleration problems • 1. A car accelerates at a rate of 20mi/hr/s. How long does it take to reach a speed of 80 mi/hr? • 2. A car travels at 60 miles per hour around a curve. Is the car accelerating? • 3. A car travels in a straight line at 60mi/hr. Is the car accelerating?

  29. Answers: 1. ∆V 80mi/hr a t 20mi/hr/s t 4sec = t 2. yes! Because it’s changing direction! 3. no! It’s not changing speed or direction!

  30. Deceleration • Negative acceleration • Example: A car slows from 60mi/hr to 20mi/hr in 4 seconds. What is its acceleration?

  31. Answer: • Acceleration = ∆V/ ∆T • Acceleration = Vf – Vi t • a = 20mi/hr – 60mi/hr 4 s a = -40mi/hr 4s a = -10mi/hr/s

  32. Review: Distance-time graph of acceleration

  33. Distance-time graph of deceleration

  34. Review:Speed-time graph of acceleration

  35. Review: Speed-time graph of deceleration

  36. Review: Distance-time graph of constant speed

  37. Momentum • Momentum = Mass x Velocity • Which has more momentum: a 300lb football player moving at 5m/s or a 200lb quarterback moving at 10m/s?

  38. Answer: • Momentum of the 300lb player is 300lbs x 5m/s = 1500lb-m/s • Momentum of the quarterback is 200lbs x 10m/s = 2000lb-m/s • The quarterback has a greater momentum!

  39. inelastic collisions

  40. Inelastic collision

  41. elastic collisions

  42. Elastic collision

  43. Two dimensional collision

  44. Momentum problems • 2 cars are heading east, car A is traveling 30mi/hr, car B is traveling 60mi/hr. Each car weighs 2000lbs. • What is the momentum of car A? • What is the momentum of car B? • If car B crashes into car A, what is the total momentum?

  45. Answers: • P=mv • Car A’s momentum = 30mi/hr x 2000lbs PA = 60,000 mi-lbs/hr east • Car B’s momentum = 60mi/hr x 2000lbs PB = 120,000 mi-lbs/hr east • Total momentum = PA + PB = 60,000 + 120,000 = 180,000 mi-lbs/hr east

  46. Another momentum problem! • Car X is traveling 30mi/hr east, car Y is traveling 60mi/hr west. Each car weighs 2000lbs. • What is the momentum of car X? • What is the momentum of car Y? • If car X crashes into car Y, what is the total momentum?

  47. Answers: • P=mv • Car X’s momentum = 30mi/hr x 2000lbs PA = 60,000 mi-lbs/hr east • Car Y’s momentum = 60mi/hr x 2000lbs PY = 120,000 mi-lbs/hr west • Total momentum = PY - PX = 120,000 - 60,000 = 60,000 mi-lbs/hr west

  48. Which has more momentum?

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