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Bellringer 9.4.14

Bellringer 9.4.14. 1. How is velocity different from speed ? 2. Which two factors (variables) determine an object’s velocity ? 3. Guess which graph below shows a constant velocity A or B?. Instantaneous Speed. Speed can be measured at a certain point in time .

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Bellringer 9.4.14

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  1. Bellringer 9.4.14 1. How is velocity different from speed? 2. Which two factors (variables) determine an object’s velocity? 3. Guess which graph below shows a constant velocity A or B?

  2. Instantaneous Speed • Speed can be measured at a certain point in time. • For instance, if you are driving, your speedometer may read 30 mi/hr. • You don’t have to drive for an hour for your car to know this – your speed is instantaneous.

  3. Velocity (Speed) • Speed is a rate for the distance traveled per unit of time • Velocity is speed in a direction • Velocity = Distance • Time • Measured in m/s (meters per second) d V t

  4. Calculating Velocity After driving for exactly 60 seconds, you have driven 600 meters. What velocity were you driving? V= d/t d=600m t= 60s v= 600m 60s v= 10 m/s

  5. Calculating Velocity / Time / Dist. You know you can drive 80 km/hr to get to the concert. The concert is 470 km away. How long will it take for you to get there? V= d/t t= ? v=80 km/hrd=470 80=470/t t=470/80 t= 5.88 hrs

  6. Constant Velocity • Constant Velocity - means an object does not speed up or slow down. • Which car is moving fastest? Which is moving at a constant speed?

  7. Graphing Constant Speed

  8. How to read a Constant Velocity Graph

  9. Motion Maps Pretend you are eating a dripping ice cream cone while you are walking What kind of motion do the drips mean? • . . . . . . . • . . . .

  10. Acceleration • Acceleration occurs when an object: • Speeds up • Slows down • **Changes direction**

  11. Acceleration • Acceleration is the rate of change of velocity

  12. Graphing Changing Speed

  13. Graphing Changing Speed

  14. Acceleration • Acceleration is found by: • a = (vf – vi) • time • The units are m/s2

  15. Calculating Acceleration A car goes from 0 m/s to 20 m/s in 6 s. What is the car’s acceleration? Vf= 20m/s Vi = 0m/s T=6s a = vf-vi t a= 20-0 = 3.33m/s² 6

  16. Calculating Acceleration 2. A man was running at 3 m/s. In 4 seconds, he slowed down so his velocity is now 1 m/s. What was his acceleration? Vf= 1m/s Vi = 3m/s T= 4s a = vf-vi t a= 1-3m/s = -0.5m/s² 4s

  17. Finding Unknowns with Acceleration 3. A bobcat starts running at 30m/s and his acceleration is 5m/s/s. What would his final velocity be if he ran for 5 seconds? Vf= ? Vi = 30m/s T= 5s a= 5m/s² a = vf-vi t 5m/s² = Vf—30m/s 5s 25=vf-30 55=vf

  18. A girl is riding her skateboard to the park, and she started out going 5m/s but by the time she got down the hill, she was going 22m/s. If her acceleration was 3m/s², how long did she ride the skateboard?

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