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Bellringer

Bellringer. January 30 th 2013 If an astronaut throws a ball in space, when will the ball stop? WRITE THE QUESTION AND ANSWER. Speed, Velocity, & Acceleration. What is speed?.

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Bellringer

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  1. Bellringer • January 30th 2013 • If an astronaut throws a ball in space, when will the ball stop? • WRITE THE QUESTION AND ANSWER.

  2. Speed, Velocity, & Acceleration

  3. What is speed? • Speed is a measure of how fast something moves or the distance it moves, in a given amount of time. The greater the speed an object has, the faster it changes position.

  4. Review • The rate at which an object moves is its speed. Speed can be calculated this way: • Speed = Distance/Time S

  5. Example • A train travels 300 km in 5 hours. Solve to find the train’s speed. S

  6. Speed Word Problems • A bug crawled 25.0 cm in 5.0 seconds. Its average speed was ______. • In 2.5 seconds, a turtle was able to travel 10.0 cm. Its average speed was _______.

  7. Speed, Velocity, & Acceleration 1. What is velocity? • Velocity is a speed in a specific direction. 2. What is acceleration? • The rate at which velocity changes with time. 3. What is the relationship between velocity and acceleration? • Acceleration is a measure of how quickly the velocity changes. If velocity does not change, there is no acceleration.

  8. The direction of accel- eration is same as direction of force. • The acceleration is proportional to the magnitude of the force. Definition of Acceleration • An acceleration is the change in velocity per unit of time. • A change in velocity requires the application of a push or pull (force). A formal treatment of force and acceleration will be given later. For now, you should know that:

  9. ACCELERATION Acceleration includes: a) Speeding up; also called acceleratingorpositive acceleration.

  10. ACCELERATION b) Slowing down; also called decelerating or negative acceleration.

  11. ACCELERATION c) Turning, which is a change of direction.

  12. F a 2F 2a Acceleration and Force Pulling the wagon with twice the force produces twice the acceleration and acceleration is in direction of force.

  13. ACCELERATION The formula to calculate acceleration is: (Final velocity) – (Starting velocity) The amount of time the change takes = Vf – Vi = Δ V t t “Change”

  14. ACCELERATION * The SI unit for acceleration is: m/s/s or m/s2 ** This is because you are dividing velocity (m/s) by time (s)

  15. Force t = 3 s + v0= +2 m/s vf= +8 m/s Example of Acceleration The wind changes the speed of a boat from 2 m/s to 8 m/s in 3 s. Each second the speed changes by 2 m/s. Wind force is constant, thus acceleration is constant.

  16. Acceleration is positive (+) or negative (-) based on the direction of force. • Positive acceleration is speeding up. • Negative acceleration is slowing down.

  17. ACCELERATION 7. Parachute example: A man jumps from a plane. His beginning speed is 100 mi/hr, and his ending speed with his parachute is 10 mi/hr. This took 3 sec. What was his acceleration? (10 mi/hr – 100 mi/hr) = -30 mi/hr/s 3s The negative sign means that he was decelerating (slowing down).

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