# Notes: d vs. t graphs E.Q.: How do position-time graphs tell us about velocity?

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Notes: d vs. t graphs E.Q.: How do position-time graphs tell us about velocity?

Zero slope = zero velocity positive slope = positive velocity negative slope = negative velocity = moving opposite way steeper slope (up or down) = higher speed Straight line = constant velocity position time slope = velocity

Notes: Velocity11/18 EQ: How do we calculate velocity?

in a direction. Velocity is speed in a direction. If speed or direction changes, velocity changes. If speed or direction changes, velocity changes.

Velocity … is the rate of change in position. v = Δd / Δt …or… (d 2 -d 1 ) (t 2 -t 1 ) v =

Example: A pumpkin is shot straight up from 5.m high to 85m high in 4.0 seconds. What was the pumpkin’s average velocity? Δd / Δt v avg = Δd / Δt (d 2 -d 1 ) / (t 2 -t 1 ) = (d 2 -d 1 ) / (t 2 -t 1 ) (85m – 5.0m)/(4.0s – 0s) v avg = (85m – 5.0m) / (4.0s – 0s) 80.m/4.0s = 80.m / 4.0s m/s upwards v avg = 20. m/s upwards

Example: Jared looks out his window and sees the pumpkin falling from 75 meters high 5.0 seconds after it was shot to 35 m high 7.0 seconds after it was shot upwards. What was the average pumpkin velocity observed by Jared? Δd / Δt = (d 2 -d 1 ) / (t 2 -t 1 ) v avg = Δd / Δt = (d 2 -d 1 ) / (t 2 -t 1 ) (35m – 75m)/(7.0s – 5.0s) v avg = (35m – 75m) / (7.0s – 5.0s) 40.m/2.0s v avg = 40.m / 2.0s m/s upwards v avg = - 20. m/s upwards …or… 20 m/s downwards

Average vs. Instantaneous Instantaneous = at one point in time Average = the mean value Average = the mean value… total distance / total time Average speed or velocity tells us nothing about speed in the middle. Example: 60 mph Everett  Lynnwood, 20 mph Lynnwood  Shoreline… 20 mph Lynnwood  Shoreline… V avg = 30 mph.

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