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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. Speed. Speed = Distance ÷ Time D_ S T

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

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

  5. 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?

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

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

  8. 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?

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

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

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

  12. Distance (m) time (sec)

  13. 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.

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

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

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

  17. 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

  18. 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

  19. 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.

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

  21. Acceleration • Change in velocity • Can be change in speed or direction • Acceleration = ∆V/ ∆T • ∆V a t

  22. 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?

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

  24. 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?

  25. 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!

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

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

  28. Review: Distance-time graph of acceleration

  29. Distance-time graph of deceleration

  30. Review:Speed-time graph of acceleration

  31. Review: Speed-time graph of deceleration

  32. Review: Distance-time graph of constant speed

  33. 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?

  34. 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!

  35. 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?

  36. 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

  37. 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?

  38. 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

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