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

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Presentation on theme: "Acceleration  The rate* at which an object’s velocity changes *rate = a change over time."— Presentation transcript:

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

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

4  Discuss with a neighbor whether it is describing acceleration or not 1.You are riding your bike at 9 km/hr. Ten minutes later, your speed is 6 km/hr 2.You ride your bike around the block at a constant speed of 11 km/hr 3.You ride your bike in a straight line at a constant speed of 10 km/hr 4.You are stopped at a red light and then it turns green

5  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 (V f ) minus initial velocity of the object (V i ) (also written as V f – V i )

6  Acceleration is a unit of speed divided by a unit of time ◦ Ex: m/s/s  Can also be written as m/s 2 ◦ Ex: km/hr/s ◦ Ex: km/hr/hr  Can also be written as km/hr 2  What does this unit mean? ◦ It tells you how much velocity is changing per unit of time  Ex: 5 m/s 2  Means that velocity is increasing (because it’s a positive #) by 5 m/s every second that the object travels

7 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 3s = 30 m/s4s = 40 m/s

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

9  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? 1. Write what is given: ◦ V i = 0 m/s (it started at rest) ◦ V f = 80 m/s ◦ ∆t = 20 s 2. Solve for acceleration:

10  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? 1. Write what is given: ◦ V i = 3 m/s ◦ V f = 0 m/s (came to a stop) ◦ ∆t = 2 s 2. Solve for acceleration:

11  Write the following numbers/units and label as either: distance, time, mass, speed or velocity mi/hr g m hr m/sec west

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