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Presentation on theme: "Acceleration."— Presentation transcript:

1 Acceleration

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

3 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

4 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

5 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)

6 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

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 4s = 40 m/s 3s = 30 m/s

8 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

9 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:

10 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:

11 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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