Measuring Motions: Speed, Velocity, and Acceleration

1. Measuring Motions: Speed, Velocity, and Acceleration 9/18/18

2. Motion is when an object changes place or position. To properly describe motion, you need to use the following: • Start and end position? • Movement relative to what? • How far did it go? • In what direction did it go? What Is Motion? https://www.youtube.com/watch?v=21BwUNDOQno

3. Speed How can we describe how fast an object moves? Example: A car on Beltway 8 travels 90 km in 1 hour. We say that the car travels ata speedof 90 km/hr.

4. Speed (S) = distance traveled (D) / the amount of time it took (T). Calculating Speed S = d/t https://www.youtube.com/watch?v=_DtDCBHEM1k

6. If I travel 100 kilometer in one hour then I have a speed of… 100 km/h If I travel 1 meter in 1 second then I have a speed of…. 1 m/s Calculating speed S = d/t

7. Graphing Speed • Speed is usually graphed using a line graph, and it depicts the distance and time. • Time is the independent variable, and thus is ALWAYS on the x-axis. • Distance is the dependent variable, and is ALWAYS on the y-axis.

8. Graphing Speed: Distance vs. Time Graphs Denver Phoenix

10. Depends, but will always be a distance unit / a time unit • Ex. Cars: mi./h = Miles per hour • Jets: km/h = Kilometers per hour • Snails: cm/s = Centimeters per second • Falling objects: m/s = Meters per second Units for speed

11. How can we describe how fast an object moves? Speed is a measure of how fast something moves. Speed = distance travelled per unit of time SI unit: m/s or km/h(for long distances)

12. Question 1 • A bug crawls 10 cm in 5 sec. What was the bug’s approximate speed in cm/sec? 2 cm/sec

13. Average speed Average speed does not tell the variations during the journey. On most trips, the speed at any instant is often different from the average speed.

14. Speed is usually NOT CONSTANT • Ex. Cars stop and go regularly • Runners go slower uphill than downhill • Average speed = total distance traveled/total time it took. Average speed

15. A car travels 300km in 6 hours. What is the average speed of the car in km/hr? • Distance: • 300km • Time: • 6hr • Ave. Speed: • s=d/t = 300 km/6 h = 50 km/h Calculating Average Speed

16. Average speed A car travels at 50 km/h, slows down to 0 km/h, and speeds up again to 60 km/. Its average speed over the whole journey overall distance travelled = total time of travel

17. ( ) Average speed = 10.49 s question The world record for women’s 100-m race is 10.49 s. What is the average speed? 100 m = 9.53 m/s

18. What is the speed of a jet plane that flies 7,200km in 9 hr ? • A) 64,800 km • B) 800 km • C) 7,191 km • D) 7,209 km • Ave. Speed: • s=d/t = 7200 km/9 h = 800 km/h Question

19. Instantaneous speed Instantaneous speed = speed at any instant The word ‘speed’ alone  instantaneous speed Instantaneous speed  distance travelled inan extremely short time interval

20. Instantaneous speed Speedometer tells the car’s speed at any instant!

21. https://www.youtube.com/watch?v=apewLkLAR-U • Velocity – the SPEED and DIRECTION of an object. • Example: • An airplane moving North at 500 mph • A missile moving towards you at 200 m/s Velocity

22. direction magnitude (speed) Velocity Velocity is... a speed in a given direction or rate of change of displacement. a vector quantity velocity

23. Velocity Speed with direction Train engineers use speed only. speed = 90 km/h Pilots use velocity (direction & speed). speed = 300 km/h direction = west

24. Average velocity overall displacement Average velocity= total time of travel direction of overall displacement direction of velocity =

25. Question • A student runs around a circular track that is 1000m in length in a time of 30 min. What is the average velocity of the student? 0 m/min If the student runs completely around the track, they are back where they began. So their overall displacement is zero.

26. Instantaneous velocity The velocity atany instant is calledinstantaneous velocity. If a car moves at a constant velocity... … its average and instantaneous velocities have the same value.

27. Question • Which of these is a correct velocity? • 55 miles per hour • 15 kilometers per second • 30 meters per second east • 400,000,000 meters per hour

28. What is the difference between speed and velocity? Speed is just distance/time. Velocity includes speed & direction as well. Question https://www.youtube.com/watch?v=ukWpTQq13dw

29. How can you determine an object’s speed and velocity? You can determine speed by using a meter stick and a stopwatch, and the determination of velocity requires a meter stick, stopwatch, and compass. Question

30. Question Average Speed = Total distance/Total time = 12 km/6 hr = 2 km/hr • Below is a distance vs. time graph of my position during a race. What was my AVERAGE speed for the entire race? Distance=12 km Time = 6 hr

31. Question • Below is a distance vs. time graph for 3 runners. Who is the fastest? Leroy is the fastest. He completed the race in 3 hours

32. Acceleration = speeding up • Acceleration – the rate at which velocity changes • Can be an: • Increase in speed • Decrease in speed • Change in direction Acceleration https://www.youtube.com/watch?v=vxFYfumAAlY

33. Acceleration When an object moves faster and faster, its speed is increasing (velocitychanged).

34. Acceleration When an object moves slower and slower, its speed is decreasing (velocity changed).

35. Acceleration When an object changes direction, its velocity changes too.

36. The formula for calculating acceleration is: Acceleration (a) = final velocity (vf) – initial velocity (vi) time (sec) The unit for acceleration, in this case, is m/s/s OR m/s2 Acceleration

37. direction speed Acceleration Acceleration measures the change in velocity Acceleration = velocity per unit time overall change in velocity = total time taken vector quantity Unit: m/s/s =m/s2

38. Increasing speed • Example: Car speeds up at green light • Decreasing speed • Example: Car slows down at stop light • Changing Direction • Example: Car takes turn (can be at constant speed) Types of acceleration screeeeech

39. 40 m/s – 20 m/s 60s – 15 s 20 m/s = 45 s Question Tommy accelerates from 20 m/s at 15 sec (t1) to 40 m/s at 60 sec (t2). What is his avg. acceleration between t1 and t2? Avg. acceleration = = .44 m/s2

40. How can a car be accelerating if its speed is a constant 65 km/h? If it is changing directions it is accelerating Question

41. Can use 2 kinds of graphs • Speed vs. time • Distance vs. time Graphing Acceleration

42. Graphing Acceleration:Speed vs. Time Graphs • Speed is increasing with time = accelerating • Line is straight = acceleration is constant

43. Graphing Acceleration:Distance vs. Time Graphs • On Distance vs. Time graphs a curved line means the object is accelerating. • Curved line also means your speed is increasing.

44. Speed=Distance ÷ Time Time=Distance ÷ Speed Distance = Speed X Times Velocity=Distance ÷ Time Time= Distance ÷ Velocity Distance=Time X Velocity Acceleration=Velocity ÷ Time Time= Velocity ÷ Acceleration Velocity=Time X Acceleration Speed/Velocity/Acceleration https://www.youtube.com/watch?v=8glfUANjBbY https://www.youtube.com/watch?v=RlFgR297o8I