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Unit 2 Section 2 NotesAcceleration
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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.
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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!
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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
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Calculating Acceleration 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
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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
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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.
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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
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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.
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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.
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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.
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