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Motion

Motion. Describing Motion. How can we describe motion? Words Pictures/Diagrams Which is better? Why?. Motion Diagrams. Motion diagrams--- a series of images showing the positions of a moving object at equal time intervals

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Motion

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  1. Motion

  2. Describing Motion • How can we describe motion? • Words • Pictures/Diagrams • Which is better? Why?

  3. Motion Diagrams • Motion diagrams--- a series of images showing the positions of a moving object at equal time intervals • -Particle Motion--- a simplified version of a motion diagram in which the object is replaced by a series of single points -size of the object must be much less than the distance it moves

  4. Motion Diagrams

  5. Vectors and Scalars • vectors are quantities that have both size (magnitude) and direction -represented by arrows • scalars are quantities that are just numbers without direction, such as distance, time and temperature • Some items in physics will be vectors (ex: velocity and acceleration) while others will be scalars (ex: distance and time)

  6. Distance • -An important part of describing the motion of an object is to describe how far it has moved, which is distance. • -The SI unit of length or distance is the meter (m). Longer distances are measured in kilometers (km).

  7. -Suppose a runner jogs to the 50-m mark and then turns around and runs • back to the 20-m mark. Displacement • The runner travels 50 m in the original direction (north) plus 30 m in the opposite direction (south), so the total distance she ran is 80 m.

  8. Displacement • -Displacement is the distance and direction of an object's change in position from the starting point. • -The runner’s displacement is 20 meters north of the starting point.

  9. Plotting a Distance-Time Graph -If we plot a distance-time graph, we can see the relationship between speed, distance and time -Time is on the x-axis and distance is on the y-axis

  10. Speed and velocity

  11. Speed • -You also might want to describe how fast it is moving. • -Speed is the distance an object travels per unit of time. • -Speed is a scalar

  12. Instantaneous Speed • -A speedometer shows how fast a car is going at one point in time or at one instant. • -The speed shown on a speedometer is the instantaneous speed. • -Instantaneous speed is the speed at a given point in time.

  13. Velocity • -Speed describes only how fast something is moving. • -To determine direction you need to know the velocity. • -Velocity includes the speed of an object and the direction of its motion. • -Velocity is a vector

  14. Velocity • -Because velocity depends on direction as well as speed, the velocity of an object can change even if the speed of the object remains constant. • -The speed of this car might be constant, but its velocity is not constant because the direction of motion is always changing.

  15. Average Velocity • the rate of change of displacement with time • -has magnitude AND direction • -average velocity is calculated by dividing the change in distance (the displacement) by the change in time (the time interval) v = (df-di)/(tf-ti)

  16. GUESS method • Given • Unknown • Equation • Substitute • Solution

  17. Problems • Whatis the velocity of a truck that travels 10. km in 10. minutes? • ANS: 17 m/s

  18. Problems • What is the average velocity of a commercial jet that travels from New York to Los Angeles (4800 km) in 6.00 hours? (convert answer to m/s) • ANS: 220 m/s

  19. Problems • A car is traveling at an average velocity of 70.0 m/s. How many km would the car travel in 6.5 hours? • ANS: 1700 km

  20. Problems • If you run 100. m at a speed of 5.0 m/s and then walk 100. m at 1.0 m/s what is your average velocity? • ANS: 1.7 m/s

  21. Problems • A rabbit and a turtle are practicing for their big race. The rabbit covers a 30. m practice course in 5.0 seconds, the turtle covers the same distance in 120 seconds. If the actual race is run on a 96 m course, by how many seconds will the rabbit beat the turtle? • ANS: 370 sec

  22. Average Velocity • We can use the velocity to determine an object’s position! • An object’s position is equal to the average velocity multiplied by time plus the initial position. • Symbol= dt • Units=m dt= vt + di

  23. Problems • What distance is traveled by a police car that moves at a constant velocity of 1.5 km/minute for 5.0 minutes? • ANS: 7.5 km

  24. Problems • What distance would be covered in 10.0 minutes by a train that travels at a constant speed of 500. meters every 10.0 seconds? • ANS: 3.00 x 104 m

  25. Problems • A tsunami caused by an earthquake occurring in Alaska in 1946 consisted of several huge waves which were found to travel at the average speed of 790 km/hr. The first of the waves reached Hawaii 4 hours 34 minutes after the earthquake occurred. From this data, calculate how far the origin of the tsunami was from Hawaii? • ANS: 4,000,000 m

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