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Motion and Force

Motion and Force. Chapter Three: Motion. 3.1 Position and Velocity 3.2 Graphs of Motion 3.3 Acceleration. Investigation 3A. Positive and Negative Position. How do we measure position in two dimensions?. 3.1 The position variable.

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Motion and Force

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  1. Motion and Force

  2. Chapter Three: Motion • 3.1 Position and Velocity • 3.2 Graphs of Motion • 3.3 Acceleration

  3. Investigation 3A Positive and Negative Position • How do we measure position in two dimensions?

  4. 3.1 The position variable • Motion is about knowing where things are and how they move. • To understand where things are, we need to understand position.

  5. 3.1 The position variable • Position is a variable and it is always relative to an origin, or the place where the object’s starting point was zero.

  6. 3.1 Forward and backward • Position and distance are similar but not the same. • Both use units of length. • Distance can have only positive values.

  7. 3.1 Forward and backward • Position uses positive and negative numbers. • Positive numbers are for positions to the right (in front) of the origin. • Negative numbers are for positions to the left (or behind) the origin.

  8. 3.1 Forward and backward • Many variables can be positive or negative. • These include position, speed, and force. • These variables are called vectorsbecause they can have a value and a direction. We use the term velocity to mean speed with direction.

  9. 3.1 Keeping track of where you are • Pathfinder is a small robot sent to explore Mars. • It landed on Mars in 1997. • Where is Pathfinder now?

  10. 3.1 Keeping track of where you are • Pathfinder keeps track of its velocity vector and uses a clock. • Suppose Pathfinder moves forward at 0.2 m/s for 10 seconds. What is Pathfinder’s velocity?

  11. 3.1 Keeping track of where you are • Suppose Pathfinder goes backward at 0.2 m/s for 4 seconds. What is Pathfinder’s velocity? What is Pathfinder’s change in position?

  12. 3.1 Keeping track of where you are • The change in position is the velocity multiplied by the time.

  13. 3.1 Keeping track of where you are • Each change in position is added up using positive and negative numbers. • Pathfinder has a computer to do this.

  14. 3.1 Maps and coordinates • If Pathfinder was crawling on a straight board, it would have only two choices for direction. • Out on the surface of Mars, Pathfinder has more choices. The possible directions include north, east, south, and west, and anything in between.

  15. 3.1 Maps and coordinates • Pathfinder’s exact position can be described with two numbers. • These numbers are called coordinates. • This graph shows Pathfinder at coordinates (4, 2) m.

  16. 3.1 Maps and coordinates • The graph can also show any path Pathfinder takes, curved or straight. • This kind of graph is called a map. • Street maps often use letters and numbers for coordinates.

  17. 3.1 Vectors on a map • Suppose you run east for 10 seconds at a speed of 2 m/s. • Then you turn and run south at the same speed for 10 more seconds. • Where are you compared to where you started?

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