Unit 2 Section 2 Notes Acceleration Acceleration v

Unit 2 Section 2 Notes Acceleration

Acceleration v Acceleration: rate of change in velocity q 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 q Acceleration is a vector quantity: includes both magnitude and direction.

Acceleration v. An object is accelerating even it its speed stays the same and only its direction changes. Why? q 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. q Therefore, you can constantly accelerate while never speeding up or slowing down!

Centripetal Acceleration v. Centripetal Acceleration: acceleration that occurs in a circular motion. q 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

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

Acceleration Values v. What do acceleration values tell you? q If acceleration is small, velocity is increasing very gradually. q If acceleration is large, velocity is increasing more rapidly. q Positive acceleration: an object’s velocity is increasing; object is speeding up q Negative acceleration: an object’s velocity is decreasing; object is slowing down

Acceleration Values v. In science, acceleration describes any change in velocity; not just speeding up q When you slow down, you have a negative acceleration because it is opposite the direction of motion.

Graphing Accelerated Motion v. When graphing acceleration: q Independent variable, which is time, is on the x- axis q Dependent variable, which is speed/velocity, is on the y-axis

Graphing Accelerated Motion v 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. v 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 q Line with a negative slope: object is slowing down q v A curved line on a distance vs. time graph means the object is accelerating.

Acceleration Sample Problems v. 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 v. Find 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/1 DKi n/U 1 L 1 e. cfm