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## Unit 2 Section 2 Notes Acceleration

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**Unit 2Section 2 Notes**Acceleration**Acceleration**• Acceleration: rate of change in velocity • An object accelerates if: • It’s speed changes: if an object is speeding up or slowing down, its acceleration is changing • It’s direction changes: if an object is traveling at the same speed but changes direction • Both speed and direction change • Acceleration is a vector quantity: includes both magnitude and direction.**Acceleration**• An object is accelerating even it its speed stays the same and only its direction changes. Why? • Acceleration is defined as the rate at which velocity changes with time; velocity includes both speed and direction, so an object accelerates if its speed, direction, or both change. • Therefore, you can constantly accelerate while never speeding up or slowing down!**Centripetal Acceleration**• Centripetal Acceleration: acceleration that occurs in a circular motion. • If you move at a constant speed in a circle, even though your speed doesn’t change, your direction does; therefore, you are accelerating. • Examples: • The moon accelerates around the earth • Riding on a Ferris wheel • Blades on a windmill • Roller coaster**To find the acceleration of an object in a straight line,**you need to measure the object’s velocity at different times. To mathematically find acceleration, take the change in an object’s velocity divided by time. or Calculating Acceleration**Acceleration Values**• What do acceleration values tell you? • If acceleration is small, velocity is increasing very gradually. • If acceleration is large, velocity is increasing more rapidly. • Positive acceleration: an object’s velocity is increasing; object is speeding up • Negative acceleration: an object’s velocity is decreasing; object is slowing down**Acceleration Values**• In science, acceleration describes any change in velocity; not just speeding up • When you slow down, you have a negative acceleration because it is opposite the direction of motion.**Graphing Accelerated Motion**• When graphing acceleration: • Independent variable, which is time, is on the x-axis • Dependent variable, which is speed/velocity, is on the y-axis**Graphing Accelerated Motion**• A straight line on a speed vs. time graph means the speed changes by the same amount over equal time intervals. This is called constant acceleration. • The slope of a straight line on a speed vs. time graph is equal to acceleration. • Line with a positive slope: object is speeding up • Line with a negative slope: object is slowing down • A curved line on a distance vs. time graph means the object is accelerating.**Acceleration Sample Problems**• Natalie accelerates her skateboard along a straight path from rest to 4.5 m/s in 2.5 seconds. Find her average acceleration.**Acceleration Sample Problems**• Find the average acceleration of a northbound subway train that slows down from 12 m/s to 9.6 m/s in 8 s.