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# Motion 2

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• ### Motion 2

1. 1. Motion & Forces <ul><li>Part II. Describing Motion </li></ul><ul><ul><ul><ul><li>Motion </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Speed & Velocity </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Acceleration </li></ul></ul></ul></ul>
2. 2. C. Acceleration <ul><li>Acceleration </li></ul><ul><ul><li>the rate of change of velocity </li></ul></ul><ul><ul><li>change in speed or direction </li></ul></ul>a : acceleration v f : final velocity v i : initial velocity t : time a v f - v i t
3. 3. C. Acceleration <ul><li>Positive acceleration </li></ul><ul><ul><li>“ speeding up” </li></ul></ul><ul><li>Negative acceleration (deceleration) </li></ul><ul><ul><li>“ slowing down” </li></ul></ul>
4. 4. D. Calculations <ul><li>A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? </li></ul>GIVEN: v i = 10 m/s v f = 32 m/s t = 3 s a = ? WORK : a = ( v f - v i ) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s 2 a v f - v i t
5. 5. D. Calculations <ul><li>A car is at a stop sign. It starts moving, and in 3 minutes is going 45 miles per hour. What is the car’s acceleration? </li></ul>GIVEN: v i = 0 mph v f = 45 mph t = 3 mins = 0.05hrs a = ? WORK : a = ( v f - v i ) ÷ t a = (45 mph – 0mph) ÷ (.05 hours) a = 45 mph ÷ .05 hrs. a = 900 mph a v f - v i t
6. 6. D. Calculations <ul><li>A cyclist bikes up a hill at an initial velocity of 25 m/s. 30 seconds later, their velocity is 10 m/s. What is the cyclist’s acceleration? </li></ul>GIVEN: v i = 25 m/s v f = 10 m/s t = 30 s a = ? WORK : a = ( v f - v i ) ÷ t a = (10m/s - 25m/s)÷(30s) a = -15 m/s ÷ 30 s a = -0.5 m/s 2 a v f - v i t
7. 7. D. Calculations <ul><li>How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s 2 ? </li></ul>GIVEN: v i = 30 m/s v f = 0 m/s a = -3 m/s 2 t = ? WORK : t = ( v f - v i ) ÷ a t = (0m/s-30m/s)÷(-3m/s 2 ) t = -30 m/s ÷ -3m/s 2 t = 10 s a v f - v i t
8. 8. E. Graphing Motion <ul><li>Acceleration is indicated by a curve on a Distance-Time graph. </li></ul><ul><li>Changing slope = changing velocity </li></ul>Distance-Time Graph
9. 9. E. Graphing Motion <ul><li>slope = acceleration </li></ul><ul><ul><li>+ velocity = acceleration </li></ul></ul><ul><ul><li>- velocity = deceleration </li></ul></ul><ul><ul><li>(negative acceleration) </li></ul></ul><ul><li>straight line (vertical) = constant acceleration </li></ul><ul><li>flat (horizontal) line = no acceleration (constant velocity) </li></ul>Velocity (m/s) Velocity-Time Graph
10. 11. C. Centripetal Acceleration <ul><ul><li>is the acceleration of objects traveling in a a circular motion </li></ul></ul><ul><ul><li>since the objects are always changing direction, so is the velocity </li></ul></ul><ul><ul><li>if the velocity is always changing, the object is accelerating (acceleration is a change in speed or direction) </li></ul></ul>