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Reference Frames

Reference Frames. What’s your point of view?. What is a Reference Frame?. Definition: A Reference Frame is a particular location that someone is making observations from. A reference frame is simply where you are, and how things look to you. What Reference Frames Do.

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Reference Frames

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  1. Reference Frames What’s your point of view?

  2. What is a Reference Frame? • Definition: A Reference Frame is a particular location that someone is making observations from. • A reference frame is simply where you are, and how things look to you.

  3. What Reference Frames Do • Reference frames can change what you see when making scientific observations. • If what you see appears to be different, then your measurements will be different too…

  4. For Example • You are sitting next to a road watching a car pass by… • What object is moving?

  5. For Example • You are sitting next to a road watching a car pass by… • From outside the car, it looks like the car is moving toward the trees. (Earth’s reference frame) • From inside the car, it looks like the trees are coming toward the car and the car is still. (Car’s reference frame)

  6. Another Example • You have the misfortune to fall from a tree… • What are the reference frames? What does the motion look like for each?

  7. Another Example • You have the misfortune to fall from a tree… • Your reference frame: The ground is coming up to hit you. • Earth’s reference frame: You are falling down.

  8. A numerical example • From the Earth’s reference frame, you observe someone riding a bicycle at 25 m/s throw a baseball, which travels at 45 m/s according to you. • Remember: This is how things look from Earth’s reference frame (sitting still). • What does the person on the bicycle see? 45 m/s 25m/s

  9. A numerical example • From the Earth’s reference frame, you observe someone riding a bicycle at 25 m/s throw a baseball, which travels at 45 m/s according to you. • If the ball is going 45 m/s, it’s only going 20 m/s fasterthan the bicyclist. • So to him, it looks like the ball’s velocity is 20 m/s, and he’s sitting still. 45 m/s 25m/s

  10. A numerical example • From the Earth’s reference frame, you observe someone riding a bicycle at 25 m/s throw a baseball, which travels at 45 m/s according to you. • Earth’s Ref. Frame Rider’s Ref. Frame Rider= 25 m/s Rider= 0 m/s Ball = 45 m/s Ball = 20 m/s 45 m/s 25m/s

  11. Sample Problem • An escalator moves passengers down into a subway station at -5 m/s. A guy who can’t afford to get a stair climber is running up the down escalator at 3.5 m/s. What is his velocity relative to the Earth? • Start by drawing a diagram of the situation…

  12. Sample Problem • An escalator moves passengers down into a subway station at -5 m/s. A guy who can’t afford to get a stair climber is running up the down escalator at 3.5 m/s. What is his velocity relative to the Earth? 3.5 m/s -5 m/s

  13. Sample Problem • An escalator moves passengers down into a subway station at -5 m/s. A guy who can’t afford to get a stair climber is running up the down escalator at 3.5 m/s. What is his velocity relative to the Earth? • The escalator is carrying the person at -5m/s. • The person is walking at 3.5 m/s. 3.5 m/s -5 m/s

  14. Sample Problem • An escalator moves passengers down into a subway station at -5 m/s. A guy who can’t afford to get a stair climber is running up the down escalator at 3.5 m/s. What is his velocity relative to the Earth? • The escalator is carrying the person at -5m/s. • The person is walking at 3.5 m/s. • The person’s velocity is -5m/s + 3.5 m/s = -2.5 m/s • -2.5 m/s DOWN the escalator 3.5 m/s -5 m/s

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