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Acceleration

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Acceleration The rate* at which an object’s velocity changes *rate = a change over time

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**Three types of Acceleration**

Positive acceleration Increase in velocity Speeding up Negative acceleration Decrease in velocity Slowing down AKA deceleration Change in direction with or without velocity change

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Is there acceleration? Discuss with a neighbor whether it is describing acceleration or not You are riding your bike at 9 km/hr. Ten minutes later, your speed is 6 km/hr You ride your bike around the block at a constant speed of 11 km/hr You ride your bike in a straight line at a constant speed of 10 km/hr You are stopped at a red light and then it turns green

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**Doing the math To find acceleration: A = ∆V t**

∆ is the greek letter delta and means “the change in” To find the change in velocity: final velocity of the object (Vf) minus initial velocity of the object (Vi) (also written as Vf – Vi)

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What’s the unit? Acceleration is a unit of speed divided by a unit of time Ex: m/s/s Can also be written as m/s2 Ex: km/hr/s Ex: km/hr/hr Can also be written as km/hr2 What does this unit mean? It tells you how much velocity is changing per unit of time Ex: 5 m/s2 Means that velocity is increasing (because it’s a positive #) by 5 m/s every second that the object travels

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What does it mean? Ex 2: if a car is accelerating at a rate of 10 m/s/s then its velocity is increasing by 10 m/s every second it is traveling 1s = 10 m/s 2s = 20 m/s 4s = 40 m/s 3s = 30 m/s

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**Some words to look out for**

Zero words Words that either mean the objects starts at rest (not in motion) or stops its motion Stop At rest At a standstill

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Let’s calculate A jet starts at rest at the end of a runway and reaches a speed of 80 m/s in 20s. What is its acceleration? Write what is given: Vi = 0 m/s (it started at rest) Vf = 80 m/s ∆t = 20 s Solve for acceleration:

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**Let’s calculate…again**

A skateboarder is moving in a straight line at a speed of 3 m/s and comes to a stop in 2 seconds. What is his acceleration? Write what is given: Vi = 3 m/s Vf = 0 m/s (came to a stop) ∆t = 2 s Solve for acceleration:

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**Warm up 9/3 (write the prompt then answer)**

Write the following numbers/units and label as either: distance, time, mass, speed or velocity 34 mi/hr 29 g 125 m 89 hr 24.5 m/sec west

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