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Unit 2: Motion-- Speed and Velocity and Acceleration

Unit 2: Motion-- Speed and Velocity and Acceleration. What’s the difference between distance and displacement?. Distance : the total magnitude traveled Displacement : the shortest distance from the starting point to the ending point

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Unit 2: Motion-- Speed and Velocity and Acceleration

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  1. Unit 2: Motion-- Speed and Velocity and Acceleration

  2. What’s the difference between distance and displacement? • Distance: the total magnitude traveled • Displacement: the shortest distance from the starting point to the ending point • Draw & label this picture on the top half of your left page

  3. What is speed? • Speed–The rate of change in distance with respect to time. • Even objects that are not moving have a speed = 0 m/s • Units: m/s, cm/s, mph • Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity.  • Scalar Quantities carry no direction information with them.

  4. What is Velocity? • The rate of change in displacement with respect to time.  • Since displacement is a vector quantity, then velocity is also a vector quantity.  • Vector Quantities have both magnitude and direction. • v=d/t • v= velocity (m/s) • d= distance (m) • t= time (s) • Draw the triangle on your left page! D T V

  5. Speed & Velocity Examples • Speed is distance divided by time • 2 cm/s • Velocity includes the direction • 2 cm/s west West

  6. What is the difference between average velocity and instantaneous velocity? • Average Velocity: The longer the time period measured, the more it leads to calculating an average velocity. • Instantaneous Velocity: The shorter the time period measured the closer it brings you to calculating an "instantaneous velocity".  Only if the time period becomes zero would we truly have an instantaneous velocity. 

  7. Using Graphs to Calculate Speed • We use graphical models to predict speed • Graphical- mathematical model • Independent on x axis; what you change/test (MIX) • Dependent on y axis; what you measure • (DRY) • Position- where an object is, including direction, compared to where it was • Distance- length w/o regard to direction • Can get speed from slope of position versus time graph • Slope = Rise/run

  8. Acceleration “Acceleration” occurs when your speed changes up or down (or when you change direction). • It is the rate speed changes • Level ground- no acceleration due to gravity • Steep down hill- acceleration due to gravity • Steeper hill= more acceleration • Deceleration is slowing down • Zero acceleration is at a constant speed

  9. Acceleration • Can use a graph to show acceleration • + slope = +acceleration (speed up) • - slope = - acceleration (slow down) • 0 slope = no acceleration • Acceleration= change in speed (cm/sec) time (sec) • a = vf-vi • t • Units: cm/sec*sec or cm/sec2

  10. Free Fall- • Drop straight down • Acceleration due to gravity 9.8 m/sec2 • Terminal Velocity- • Highest velocity reached by a falling object • When an object stops accelerating, but continues to fall • When air resistance balances the pull of gravity

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