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Acceleration Unit 1 Lesson 2

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**Acceleration Velocity is the speed in a certain direction**

The rate at which velocity changes is acceleration. Velocity is the speed in a certain direction An object accelerates if its speed, direction, or both change. The amount of acceleration is dependent on how much velocity changes and how much time that change takes

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**Calculating Average Acceleration**

(final velocity – starting velocity) / time The standard units of acceleration are meters per second squared (m/s2) Dividing a velocity unit (m/s) by time (s)

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**Positive/Negative Acceleration**

Acceleration refers to both increases and decreases in speed. A change in direction is also acceleration. An increase in velocity is called positive acceleration. (speeds up) A decrease in velocity is called negative acceleration. (slows down) A negative number shows negative acceleration.

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**Centripetal Acceleration**

An object traveling in a circular motion is always changing its direction, and so it always experiences acceleration. Centripetal acceleration is acceleration in a circular motion.

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**Formative Assessment- do you understand?**

Suppose a car travels at a steady velocity. Will there be any acceleration? Why or why not? If a car gains speed as it backs up, is it demonstrating acceleration? Does the car in questions one demonstrate positive or negative acceleration? Explain. What is an example of negative acceleration? If a bird changes direction, does it demonstrate acceleration? Why or why not? What kind of acceleration does an arrow shooting out of a bow demonstrate? What kind of acceleration does a car that has run out of gas demonstrate as it rolls to a stop?

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**Acceleration Example Time Distance 0.5 24 3 48 6 72**

Create a distance time graph for the toy car Time Distance 0.5 24 3 48 6 72 72 48 24 Distance (cm) Time (seconds)

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**Velocity is the change in distance/change in time**

Acceleration Create a velocity time graph for the toy car (convert the distance time graph to velocity) Velocity is the change in distance/change in time

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**(Distance Change) / Time change**

Velocity (Distance Change) / Time change 0 s 0 cm - 0.5 s 24 cm 48 cm / sec (24 – 0)/( ) 3 s 48 cm 9.6 cm / sec (48 – 24) / ( ) 6 s 72 cm 8 cm / sec (72 – 48) / (6 - 3)

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**(Distance Change) / Time**

Velocity/Time Graph Time Distance Velocity (Distance Change) / Time - 0.5 24 48 cm / sec (24 – 0)/( ) 3 48 9.6 cm / sec (48 – 24) / ( ) 6 72 8 cm / sec (72 – 48) / (6 - 3) Velocity (cm / sec) 72 48 24 Time (seconds)

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**Interpreting the graph**

Velocity (cm / sec) When is the car accelerating? 72 48 24 Time (seconds)

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**Interpreting the graph**

When is the car accelerating? During the whole run When is the car positively accelerating? Negatively? Velocity (cm / sec) 72 48 24 Time (seconds)

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**Interpreting the graph**

When is the car positively accelerating? Negatively? Positive: During the first 0.5 second (positive slope- going up) Negative: After 0.5 seconds (negative slope- going down) Velocity (cm/ sec) 72 48 24 Time (seconds)

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**Interpreting the graph**

What would the graph look like if the car was not accelerating (positively or negatively)? Velocity (cm/ sec) 72 48 24 Time (seconds)

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**Interpreting the graph**

What would the graph look like if the car was not accelerating (positively or negatively)? Straight line Velocity (cm / sec) 72 48 24 Time (seconds)

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**Average Acceleration Calculations**

Calculate the average acceleration (final velocity – starting velocity) / time 0 seconds and 0.5 seconds? 0.5 seconds and 3 seconds? 3 seconds and 6 seconds? 0 seconds and 6 seconds? Time Distance Velocity (Distance Change) / Time - 0.5 24 48 cm / sec 3 48 9.6 cm / sec 6 72 8 cm / sec

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**Average Acceleration Calculations**

Calculate the average acceleration (final velocity – starting velocity) / time 0 seconds and 0.5 seconds? (48 – 0) / (0.5 – 0) = 96 cm / s2 0.5 seconds and 3 seconds? (9.6 – 48) / (3 – 0.5) = cm / s2 Time Distance Velocity (Distance Change) / Time - 0.5 24 48 cm / sec 3 48 9.6 cm / sec 6 72 8 cm / sec

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**Average Acceleration Calculations**

Calculate the average acceleration (final velocity – starting velocity) / time 3 seconds and 6 seconds? (8 – 9.6) / (6 – 3) = cm / s2 0 seconds and 6 seconds? (8 – 0) / (6 – 0) = 1.33 cm / s2 Time Distance Velocity (Distance Change) / Time - 0.5 24 48 cm / sec 3 48 9.6 cm / sec 6 72 8 cm / sec

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