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Understanding Motion: Frame of Reference and Speed Concepts

Explore the concept of frame of reference, distance, displacement, speed, and velocity. Learn how to measure motion relative to a frame of reference and calculate speed using average and instantaneous measures. Understand the difference between distance and displacement and how velocities are combined. Enhance your understanding with practical examples and assessments.

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Understanding Motion: Frame of Reference and Speed Concepts

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  1. Chapter 11 Motion You will need a calculator for this chapter!

  2. Section 11.1Distance and Displacementp. 328

  3. What is a frame of reference? How fast was the boat traveling? Relative to what? Motion must be described relative to a frame of reference relative motion Relative to Earth’s surface (understood)

  4. How fast was the boat traveling? Relative to spectators? Really Fast!!!! Relative to driver? ZERO! Driver & boat…same frame of reference Tennis ball ex…(p.329) Einstein’s Theory of Relativity – 10:06

  5. Choosing a Frame of Reference Conclusion?? The Frame of Reference determines how motion of an object is described.

  6. Measuring Distance Distance - length btwn 2 pts SI unit….meter (m) Derived units cm (snail crawling) km (distance btwn 2 cities)

  7. Measuring Displacements distance v.s. displacement? “walk 5 blocks” (distance ) “walk 5 blocks north from the bus stop” (displacement) – direction & distance from start to end Displacement needed for accurate directions

  8. Combining Displacements Vector? Measurement w/ magnitude and direction Magnitude? Size, length, amount Described w/

  9. Displacement along a straight line 2 vectors… same direction Add magnitudes Ex. A car travels 10 km north, stops to refuel, then travels 20 km north total distance = 30 km total displacement = 30 km (10 km north + 20 km north) from starting pt

  10. Displacement along a straight line 2 vectors…. opposite directions Subtract mags Ex. Bicyclist travels 5 km east, turns around and travels 3 km west Bicyclists total distance = 8 km total displacement = 2 km east (5 km – 3 km)

  11. Displacement That isn’t along a straight path 2+ vectors w/ different directions Combine bygraphing Resultantvector- sum of all vectors Shows distance & displacement related but different

  12. Section 11.1 Assessment What is a frame of reference? How is it used to measure motion? How are distance and displacement similar and different? How are displacements combined? A girl who is watching a plane fly tells her friend that the plane isn’t moving at all. Describe a frame of reference in which the girl’s description would be true.

  13. Section 11.1 Assessment Should your directions to a friend for traveling from one city to another include displacements or distances? Explain your choice. A spider is crawling on a wall. First it crawls 1 m up, then 1 m to the left, and then 1 m down. What is the distance the spider crawled? What is the spider’s displacement?

  14. Section 11.2 Speed and Velocityp. 332 Have your calculator on your desk

  15. Video Can you describe the speed of the skaters? What information is needed to determine the speed of the skaters? Speed- ratio of distance traveled to time needed to travel that distance. SI unit meters per second (m/s) derived units: km/hr cm/s

  16. Average speed Average Speed = total distance total time Or….. v = d t Calculating average speedMath Skills p. 333 • entire duration of a trip, • average speed- total distance traveled (d), divided by total time (t)

  17. Average Speed ( v ) Calculating average speedMath Practice p. 333 • Avg speed doesn’t reflect most common speed of trip • stops, curves, hills • Useful – tells how long trip will take • If v is60 mi/hr& destination is 120 mi, your TOA is 2 hours

  18. Instantaneous speed Instantaneous speed (v)-rate object is moving at given moment speedometers show instantaneous speed 100 mi/hr(160 km/hr)

  19. Distance-time graph Slope = change in vertical axis change in horizontal axis Slope is speedof object plotted Graphing Motion

  20. Graphing Motion Distance v.s. Time of an RC car Slope (rise/run) = speed Calculate: What can you conclude about the speed of the RC car?

  21. Graphing Motion Distance-time graph Driving speed of a car in rush hour traffic D C B A 4 segments (A-D) to find average speed for each segment Calculate: Describe the speed of the car in segment B?

  22. Velocity • Pilots and control tower communicate describing velocity of planes • Velocitydescribes speedand direction • vector • v changes if speed, direction, or both change

  23. Velocity • Car traveling at constant speed (55 mi/hr) • How would you describe its velocity? • Direction changing on circular track, velocity changing

  24. Changing Velocities Calculate: 16 km/hr east 7 km/hr east • When velocities in same direction, add together • River velocity= 7km/hr east • Boat velocity= 16km/hr east

  25. Changing Velocities a2 + b2 = c2 Calculate: 400 km/hr west 25 km/hr south When velocities at rt angles, use Pythagorean theorem to solve plane= 400km/hr west wind speed= 25km/hr south Science of NHL hockey – vectors 4:29

  26. Section 11.2 Assessment You and a friend are watching a baseball game on ESPN where the commentator says “the pitcher’s velocity of 100 mi/hr is virtually unhittable”. Your friend agrees. What do you think? What does the slope on a distance-time graph indicate?

  27. Section 11.2 Assessment Does a car’s speedometer show instantaneous speed, average speed, or velocity? Explain. An Olympic swimmer swims 50.0 meters in 23.1 seconds. What is his average speed?

  28. Section 11.2 Assessment A plane’s average speed between two cities is 600 km/hr. If the trip takes 2.5 hours, how far does the plane fly?

  29. Section 11.2 Assessment A discus thrower threw his disc 139 meters through the air. While in flight, the disk traveled at an average speed of 13.0 m/s. How much time did the disk remain in the air?

  30. Section 11.3Acceleration p. 342 Have your calculator on your desk Suzuki Hayabusa

  31. What is acceleration? it takes time • Remember velocity is speed w/ direction • Acceleration- rate velocity changes • Vector • What is a rate?

  32. Changes in speed vectors_car_velocity_accel.notebook • green stoplight car moves forward • acceleration (positive change in car’s speed) pushes you back in seat • red stoplight  speed decreases • (negative change) you fall forward towards dash

  33. Free-Fall Free-fall- acceleration toward Earth b/c gravity Speed/velocity SI units is m/s Units for acceleration - meters per second per second orm/s2 The 2nd “second” is time needed to change speed (rate)

  34. Free-Fall • a near Earth =9.8 m/s2 • bungee jumper will accelerate 9.8 meters per secondevery secondhe’s in FF • 1 s of FF speed = 9.8 m/s • 2 s of FF speed =19.6 m/s (sped up 9.8 m/s in 1 s) • What is speed after 3 s? 29.4 m/s after 3 seconds

  35. If the Earth is moving, why can I not feel it? • body detectschangesin speed • Earth spin constant speed • 850 mi/hr at mid latitudes (faster at equator) • Revolves 67,000 mi/hr • 2x bullet speed! • 1.6 million miles / day! WOW!!!

  36. Changes in Direction • a occurs if direction changes even if speed constant • Ferris wheel & carousel = constant speed • accelerate b/c change direction

  37. Changes in speed and direction • roller coasters • winding roads

  38. Constant Acceleration Indy car pulling G’s 3:00 straight line motion & speeding up / slowing down -constant acceleration v of object changes same amteach sec

  39. Calculating Acceleration Acceleration = change in velocity total time or….. (vf – vi) t (vf – vi) Velocity and acceleration 1:58 a x t calculate acceleration for straight-line motion using this equation: venn diagram review.notebook

  40. Math Practice #1 p. 346 A car traveling at 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration?

  41. Math Practice #2 p. 346 An airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s2. What is its change in velocity during this time?

  42. Math Practice #3 p. 346 A child drops a ball from a bridge. The ball strikes the water under the bridge 2.0 seconds later. What is the velocity of the ball when it strikes the water?

  43. Math Practice #4 p. 346 A boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was the rock going when it left the boy’s hand?(acceleration is downward b/c of gravity, but velocity is upward)

  44. Acceleration of a Mercedes-Benz Volunteer timers – we will average the times How much time does it take to go from 0 km/hr to 200 km/hr?

  45. Graphs of Accelerated motion Speed-time graph displays acceleration Slopeof speed-time graphis acceleration of object

  46. Distance-Time Graphs • Accelerated motion is represented by a curved (non-linear) line on distance-time graph • Slope (speed) greater after 3 sec than 1 sec acceleration video 3:24

  47. Instantaneous Acceleration Instantaneous acceleration(IA)- how fast velo changing at specific instant Skateboarder continually changes speed & direction hisIAalways changing

  48. Instantaneous Acceleration Vector of skateboarder’s acceleration can point any direction Vector length represents how fast velocity is changing IA even if standing still and acceleration vector zero

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