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Changing Velocity Sadly, most things do not always move at a constant velocity. Every object in motion was AT REST at one time, and will be at rest again!! We’ll worry about what started it moving and what will stop it, later. For now, we just care about the fact that it has started and stopped

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In this motion map below, the arrows are all the same size, and point in the same direction Changing Velocity v1v1 v2v2 v3v3 v4v4 v5v5

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Acceleration- the change in velocity wrt time –Could be increase or decrease in, or turning symbol: direction matters, so it’s a vector units: or OVER

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Changing Velocity

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Just a couple of things… For velocity, we usually use the terms “slow” and “fast” For acceleration, we should use the terms “peppy” and “sluggish”

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Acceleration & Graphs position vs. time looked like this: Velocity vs. Time looked like this How would an acceleration vs. time graph look?

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Recall that for our cart on the ramp, the position vs. time looked like this: Velocity vs. Time looked like this How would an acceleration vs. time graph look? For Position Graphs phbbt! forward zhoop forward ski slope backward downer backward

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Example! Gladys is skateboarding. She starts from rest and attains a velocity of 10 m/sec in 2 seconds. She stays at that velocity for 5 seconds, and then stops in 3 seconds. Velocity (m/sec) 0 1 2 3 4 5 6 7 8 9 Position (m) Acceleration (m/sec/sec) -5 -4 -3 -2 -1 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 Time (sec) 0 1 2 3 4 5 6 7 8 9 Time (sec) 0 1 2 3 4 5 6 7 8 9 Time (sec)

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For an object at rest, it has to increase it’s velocity, increasing the size of the velocity vector That makes the distance between each position increase at equal time intervals v1v1 v2v2 v3v3 v4v4 v5v5 Changing Velocity 0 sec1 sec2 sec3 sec4 sec5 sec

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Acceleration & Motion Maps We will always assume that if there is an acceleration, it is a CONSTANT ACCELERATION! On a motion map: 1.Acceleration vectors start ABOVE or BELOW each position mark. 2.Compare 2 consecutive velocity vectors. The acceleration vector ALWAYS points toward the larger velocity! v1v1 v2v2 v3v3 v4v4 v5v5 a2a2 a3a3 a4a4 a1a1 0 sec1 sec2 sec3 sec4 sec5 sec

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Graphing Motion, Speed and Velocity. Graphs of Motion A Distance vs. time graph that is a straight line........ always means the object moves the same.

Graphing Motion, Speed and Velocity. Graphs of Motion A Distance vs. time graph that is a straight line........ always means the object moves the same.

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