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Motion

Motion. Motion is a change in an object’s position relative to a reference point. Definition. Motion is Relative. Relative – it is described compared to a REFERENCE POINT Example: As a car drives away from school its position is changing relative to school. Describing motion .

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Motion

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  1. Motion

  2. Motion is a change in an object’s position relative to a reference point. Definition

  3. Motion is Relative • Relative – it is described compared to a REFERENCE POINT • Example: As a car drives away from school its position is changing relative to school.

  4. Describing motion • We describe motion in words, with graphs and using mathematical quantities. • The mathematical quantities we use to describe motion are distance, time, speed, velocity and acceleration.

  5. Describing motion • These mathematical quantities have certain SI units.

  6. Speed: We are concerned with 3 different types of speed. • Speed is the rate of change in position. • We will talk about average speed, instantaneous speed, and constant speed.

  7. Speed: Average Speed • Total distance traveled divided by the time interval during which the motion occurred. • s= d / t • t = d / s • d = s x t Example: If you travel 200 miles In 4 hours, your average speed is 50 mph.

  8. SpeedInstantaneous Speed • Speed at any instant Example: In your trip, you might be going 60 mph one moment and Slowing down and stopping for a break a few moments later.

  9. SpeedConstant Speed • Speed that does not change • Instantaneous speed that does not change • When an object has a constant speed, its average speed and instantaneous speed will be the same.

  10. Velocity • Speed AND direction • This is important for a full description of motion • Pilots need to know wind speed and direction. • Calculations of velocity are different than speed. • v= change in position / time

  11. Velocity: Direction matters • Imagine that two birds leave the nest at the same time. The both fly at 10 km/h for 5 min, 12 km/h for 8 min, and 5 km/h for 10 min. Why don’t they end up at the same place?

  12. A swimmer swims 50 m in 40 s. What is the swimmer’s average speed? Problem

  13. A swimmer swims 20 m in 40 s. What is the swimmer’s average speed? S = D/T S = 50m/40s S = 1.25m/s

  14. What is the average speed (mph) for a car journey of 120 miles that began at 09:30am and finished at 12:00 noon? Problem

  15. What is the average speed (mph) for a car journey of 120 miles that began at 09:30 and finished at 12:00 noon? S = D/T D = 120 T = 2.5 hours (from 9:30 – 12:00) S = 120m / 2.5h S = 48 mph Problem

  16. How far does a bicycle travel at a speed of 6 m/s for 15 seconds?

  17. How far does a bicycle travel at a speed of 6 m/s for 15 seconds? s=d/t 6m/s = d/15s 15s (6m/s) = d/15s (15s) 90 m = d

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