Usain Bolt is the world’s fastest man!!!

1. Usain Bolt is the world’s fastest man!!!

2. Physics of Motion • We will look at: • Position • Distance • Displacement • Speed • Velocity • Acceleration • First you need to realize that motion is relative…

3. Motion is relative • What is meant by saying that motion is relative? For everyday motion, what is motion usually relative to?

4. Motion is Relative • Motion is relative to the observer’s position and their reference point • Sometimes called a “reference frame” • Consider the picture… • If this man is driving at 15 mph, how fast is his coffee cup moving? • Does the man feel like the cup is moving? • Why?

5. Motion is relative • An object is in motion if it changes position relative to a stationary reference point. Use this to establish a COORDINATE SYSTEM • pick an origin or 0 point • decide which direction is positive

6. Direction • We use N, S, E, W or left, right, up, & down to describe the direction of movement. • We can also use POSITIVE and NEGATIVE to describe direction.

7. POSITION A location with respect to the origin or zero point.

8. Finding Position 4 miles 6 miles 0 4 10 -4 0 6 -10 -6 0 Position depends on where you put ‘0’.

9. Distance and Displacement • Distance measures the actual path an object takes • Displacement measures your overall distance from the initial position to final position in a STRAIGHT LINE. • DISPLACEMENT values must include a DIRECTION! • Which color line represents distance? • Displacement?

10. Speed vs Velocity: Scalars vs Vectors All measured quantities can be classified as being either a scalaror a vector. Scalar _________ only (size of the quantity ….a number) Vector _________ and _________ Magnitude Magnitude Direction

12. Distance vs. Displacement • http://physics.info/displacement/

13. Write in your own words- what is the difference between distance and displacement? • Distance- • Displacement-

14. Use the diagram to determine the resulting displacement and the distance traveled by the skier during these three minutes.

15. Answer • The skier covers a distance of • (180 m + 140 m + 100 m) = 420 m and has a displacement of 140 m, right or east.

16. Formula for Displacement How did you calculate displacement- write a formula! ∆X = Xf-Xi Xf= final position Xi= initial position Remember- displacement can be positive or negative! (ex- what if you started at “B”?)

17. What is the coach's resulting displacement and distance of travel?

18. Answer • The coach covers a distance of • (35 yds + 20 yds + 40 yds) = 95 yards and has a displacement of 55 yards, left or -55 yards.

19. Speed • Describes how fast an object moves. • We know some things move faster than others…but how do we measure it? • What two quantities must you know to determine speed?

20. What two quantities must you know to determine speed? • Choose from: displacement, distance, time, velocity • Hint…what is speed measured in??? • Speed= distance/time • Ex- miles/hour, m/s, etc.

21. There are three types of speed you must know… • Constant speed • Average speed • Instantaneous speed

22. Constant Speed • When an object covers equal distances in equal amounts of time • Ex- if a race car travels at a CONSTANT SPEED of 96m/s, it will travel a DISTANCE of 96 meters EVERY SECOND.

23. But most objects do not travel at a constant speed. • The speed of an object can change from one minute to another. • So we can use AVERAGE SPEED to describe its motion. • Use this equation… Average Speed = total Distance / total Time

24. Let’s try it • A runner finished a 3 mile race in 22 minutes. He may not have run at the same pace the whole time, but you can still calculate his AVERAGE SPEED • 3 miles/22 minutes=.14 miles/min PACE: • 22 minutes / 3 miles = 7.33 min/mile

25. Instantaneous vs. Average speed • Average speed-overall distance over time the object traveled • Instantaneous speed- measures speed over small time interval (at an instant)

26. Does a speedometer of a car read instantaneous or average speed?

27. What 2 controls on a car enable a change in speed?

29. What if I want to describe speed AND direction? • For example…what if you wanted to find a plane. Knowing the speed would only tell you how far away to look but not in what direction. For that we need… • VELOCITY- the speed and direction of motion.

30. Let’s get back to the car example… • Name another control that enables a change in velocity.

32. So…What is the difference between speed and velocity? • SPEED- reports the magnitude of distance over time (just the number). • VELOCITY- reports the magnitude AND direction of motion.

33. So how do you calculate speed vs velocity? • Speed = distance / time • Velocity = displacement / time (Includes a direction!)

34. Are speed and velocity always going to be the same? • NO! • Only if the object is moving in the SAME direction the whole time. • What is an example of a motion where avg speed is not equal to average velocity? (demo)

35. Let’s look closer… • Average velocity is calculated by the equation: Vavg= (xf-xi) / (tf-ti)

36. Use the diagram to determine the average speed and average velocity between the following points. A. Going from A and BB. Going from A to B and ending at C

37. Answers: • A. Between A and B, speed and velocity will be the same because they are in the same direction the whole time. • Speed = 180 m/min • Velocity = 180 m/min east • B. When the motion continues to point C, the speed and velocity are different because the distance traveled and displacement are different. • Speed= 320 m/2 min= 160 m/min • Velocity= 40 m/2 min= 20 m/min east

38. What is the coach's resulting displacement and distance of travel?

39. Let’s use our math skills • Page 323… • Read through “MATH SKILLS” • DO problems 1-3 “Practice Problems”

40. Answers to problems on 323 • 1. v=d/t 110m/72 sec= 1.5 m/s toward shore • v=d/t 38m/1.7 sec= 22m/s toward first base • d=vt=(12.0 km/hr)(5.00 hr) =60.0 or 6.00 x 104 m southwest

41. Acceleration Chapter 10.2-3

42. Try to define the word “acceleration”… • Actual definition is…any change in VELOCITY

43. More specifically: Acceleration is a change in velocity in a period of time. • So…Is it a vector or a scalar quantity? • VECTOR • It must include a direction (like velocity) • This also means that you can change acceleration by changing what? • Speed or Direction

44. Does travel at a constant speed mean you are not accelerating? • NO!!! • Remember that you can change velocity by changing direction, thus CHANGING ACCELERATION!

45. When a ferris wheel goes up and around, what about its passengers is changing? • Speed • Velocity • Acceleration • None of the above

46. So let me get this straight… • Constant Speed means – • Something travels the same distance in each time interval • Constant Velocity means- • Something travels the same distance, in the same direction in each time interval • So what about constant acceleration?

47. Constant Acceleration • The velocity changes by the same amt over each time interval. (figure 11, p 329) • Ex- centripetal acceleration • As the earth goes around the sun, it travels at a constant speed • BUT since it is going in a circle, it’s velocity is changing AT A CONSTANT RATE…therefore… • CONSTANT ACCELERATION!

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

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

50. What do the numbers mean? • Small acceleration – means speed is increasing slowly • Large acceleration- means speed is increasing rapidly Extension: • Acceleration can be positive or negative, but negative acceleration doesn’t always mean the object is slowing down. • (it could also be changing direction)