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Physics Fundamentals

Motion in One Dimension. Physics Fundamentals. How physicists describe motion:. Displacement, not distance. Position-time graph. Velocity, not speed. Slope: steeper means faster. Distance: The separation between two points. A scalar quantity.

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Physics Fundamentals

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  1. Motion in One Dimension Physics Fundamentals

  2. How physicists describe motion: • Displacement, not distance • Position-time graph • Velocity, not speed • Slope: steeper means faster

  3. Distance: The separation between two points. A scalar quantity.

  4. Displacement: Change in position. A vector quantity.

  5. In one dimension, there are only two possible directions. For example: Right or left In physics, we use Positive or negative Northeast or Southwest Up or down

  6. Meet Mr. Morris Shun (His friends call him Moe.)

  7. Watch Moe go … What was his displacement? One meter. -1 m 0 m 1 m

  8. Check this out … What was Moe’s displacement? Negative two meters. -1 m 0 m 1 m

  9. Gettin’ jiggy now … What was Moe’s displacement? Zero meters. -1 m 0 m 1 m

  10. Let’s graph it! position (m) 1 0 time (s) -1 0 m 1 m -1 m

  11. Velocity: Displacement per unit of time. A vector quantity. Δx v = Δt (The Greek letter Δ – delta – means “change in”) In one dimension, velocity will be either positive or negative.

  12. What was Moe’s average velocity for the first second? position (m) 1 Rise = 1 m 0 2 3 1 Run = 1 s time (s) -1 m Rise Displacement 1 m 1 Velocity = = = = s 1 s Time Run

  13. Slope = rise/run. In a position-time graph, the slope of the line gives us the object’s velocity. In other words, the steeper the line, the faster the object is moving

  14. The sign of the slope gives you the direction of the object. Lines that go from lower left to upper right have positive slope and positive velocity. The object is moving forward. Lines that go from upper left to lower right have negative slope and negative velocity. The object is moving backward.

  15. What is the velocity if the line is horizontal? Zero. The rise is zero because the displacement is zero. Slope = rise/run, and zero divided by anything is zero. The object is not moving.

  16. What do you have if the line is vertical? A mistake. The run is zero. Slope = rise/run, and you can’t divide by zero. A vertical line would mean the object was at many different positions at the same time.

  17. What was Moe’s average velocity for the last two seconds? Position (m) 1 0 2 3 1 Rise = − 2 m time (s) -1 Run = 2 s m Displacement Rise - 2 m -1 Velocity = = = = s Run 2 s Time

  18. What was Moe’s average velocity over all three seconds? Displacement (m) 1 0 2 3 Rise = − 1 m 1 Time (s) Run = 3 s -1 m Displacement Rise - 1 m - 0.3 Velocity = = = = s Run 3 s Time

  19. Moe knows … • Displacement is change in position. • It’s a vector quantity. • Velocity is displacement per unit of time. • It’s also a vector quantity. • The slope of a line on a position-time graph • equals the velocity of the object in motion.

  20. Get ready to say goodbye to Moe!

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