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Unit 2 Section 2 NotesAcceleration

AccelerationAcceleration: rate of change in velocityAn object accelerates if:Its speed changes: if an object is speeding up or slowing down, its acceleration is changingIts direction changes: if an object is traveling at the same speed but changes directionBoth speed and direction changeAcceleration is a vector quantity: includes both magnitude and direction.

AccelerationAn 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 AccelerationCentripetal Acceleration: acceleration that occurs in a circular motion.If you move at a constant speed in a circle, even though your speed doesnt change, your direction does; therefore, you are accelerating. Examples:The moon accelerates around the earthRiding on a Ferris wheelBlades on a windmillRoller coaster

Calculating AccelerationTo find the acceleration of an object in a straight line, you need to measure the objects velocity at different times. To mathematically find acceleration, take the change in an objects velocity divided by time.

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Acceleration ValuesWhat 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 objects velocity is increasing; object is speeding upNegative acceleration: an objects velocity is decreasing; object is slowing downAcceleration ValuesIn science, acceleration describes any change in velocity; not just speeding upWhen you slow down, you have a negative acceleration because it is opposite the direction of motion.

Graphing Accelerated MotionWhen graphing acceleration:Independent variable, which is time, is on the x-axisDependent variable, which is speed/velocity, is on the y-axis

Graphing Accelerated MotionA 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 upLine with a negative slope: object is slowing downA curved line on a distance vs. time graph means the object is accelerating.

Acceleration Sample ProblemsNatalie accelerates her skateboard along a straight path from rest to 4.5 m/s in 2.5 seconds. Find her average acceleration. Acceleration Sample ProblemsFind the average acceleration of a northbound subway train that slows down from 12 m/s to 9.6 m/s in 8 s. http://www.physicsclassroom.com/Class/1DKin/U1L1e.cfm