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

Usain Bolt is the world’s fastest man!!!. Physics of Motion. We will look at: Distance Displacement Speed First you need to realize that motion is relative…. Motion is relative. What is meant by saying that motion is relative? For everyday motion, what is motion usually relative to?.

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

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

  2. Physics of Motion • We will look at: • Distance • Displacement • Speed • 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. Direction • We use N, S, E, W to describe the direction of movement.

  6. Distance and Displacement • Distance measures the actual path an object takes • Displacement measures your overall distance from the starting point in a STRAIGHT LINE. • DISPLACEMENT values must include a DIRECTION! • Which color line represents distance? • Displacement?

  7. Distance vs. Displacement • http://www.physics.gatech.edu/academics/classes/2211/main/demos/displacement/DDis.html

  8. 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?

  9. 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.

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

  11. But first let’s look at some graphs… • If I wanted to graph speed, what should I label my axes??? • So the slope of the line=SPEED Distance Speed Time

  12. 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.

  13. Constant Speed • What would a d-t graph look like for a constant speed?

  14. 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

  15. 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 • 22 minutes / 3 miles = 7.33 min/mile

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

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

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

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

  20. 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) = 6.00 x 104 m

  21. 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.

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

  23. In order to analyze such situations, we need to understand what are known as 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

  24. Speed is Velocity…kind of… • Velocity is the vector for the scalar of speed. • The magnitude is the same!!! • Therefore in calculations, you can use speed or velocity interchangeably • Speed = distance / time • Velocity = distance / time in a direction • http://www.youtube.com/watch?v=DRb5PSxJerM&feature=related

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

  26. Answer • The skier covers a distance of • (180 m + 140 m + 100 m) = 420 m and has a displacement of 140 m, rightward.

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

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

  29. Consider a car moving with a constant, rightward (+) velocity of 10 m/s. • How many meters will he travel in 5 seconds?

  30. Constant velocity

  31. Now consider a car moving with a rightward (+), changing velocity - that is, a car that is moving rightward but speeding up or accelerating.

  32. Acceleration

  33. Distance time graphs • Draw 2 graphs • One showing a slow constant speed • One showing a faster constant speed

  34. Consider a car moving with a constant, rightward (+) velocity - say of +10 m/s. A car moving with a constant velocity is a car with zero acceleration. • Draw a graph!

  35. Constant velocity = zero acceleration

  36. Now consider a car moving with a rightward (+), changing velocity - that is, a car that is moving rightward but speeding up or accelerating. Since the car is moving in the positive direction and speeding up, the car is said to have a positive acceleration.

  37. Positive acceleration

  38. Describe this graph!

  39. Does the velocity of the wind affect such things as a sprinter’s speed or an airplane’s flight time?

  40. Resultant Velocity animation • http://www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/vectors/plane.html

  41. “Adding Vectors” Example: • A small airplane headseast with a speed of 200 mphwith respect to the air (the “air speed”). This would be the plane’s speed if the air was NOT moving – no wind) • If the wind/jet stream is moving east at 50 mph, what is the plane’s resulting velocity with respect to the ground (the “ground speed”)? 200 50 250 mph, east with the wind

  42. If, later, the airplane is flying westinto the 50 mph wind with an “air speed” of 200 mph, now what is the plane’s resulting velocity with respect to the ground (the “ground speed”)? 200 50 150 mph, west against the wind

  43. Find the velocity in m/s of a swimmer who swims 110 m toward the shore in 72 s.

  44. 1.5 m/s toward the shore

  45. Imagine that you could ride a baseball that is hit high enough and far enough for a home run. Using the baseball as a reference frame, what does the Earth appear to do?

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