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Acceleration

Acceleration. Acceleration is another way to measure and describe the motion of an object. Acceleration : (a) rate of change of velocity over time. An object is considered to be accelerating when it speeds up , slows down , or changes direction .

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Acceleration

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  1. Acceleration Acceleration is another way to measure and describe the motion of an object. • Acceleration: (a) rate of change of velocity over time. • An object is considered to be accelerating when it speeds up, slows down, or changes direction. • Measured in mi/hr2, m/s2, km/hr2, etc. • Positive acceleration: when an object speeds up • Negative acceleration: when an object slows down. vf - vi a = t vf = final velocity vi = initial velocity

  2. Example #1 A car traveling 35 km/hr accelerates to a speed of 45 km/hr in 0.25 hr. What is its acceleration? vi = 35 km/hr vf = 45 km/hr t = 0.25 hr a = ? a = vf - vi t a = (45 – 35) 0.25 a = 10 . 0.25 a = 40 km/hr2

  3. Example #2 A jet is traveling at 80 m/s when it starts to approach a runway. It is able to land and park in 10 s. What is its acceleration? vi = 80 m/s vf = 0 m/s t = 10 s a = ? a = vf - vi t a = (0 – 80) 10 a = -80 . 10 a = -8 m/s2 The negative acceleration makes sense because the jet is slowing down as it comes to a stop.

  4. Example #3 A skateboarder has an acceleration of 1.5 m/s2. Starting from rest, if he accelerates for 2 s, what speed will he reach? a = 1.5 m/s2 vi = 0 m/s t = 2 s vf = ? a = vf - vi t at = vf– vi at + vi = vf vf = at + vi vf = (1.5)(2) + 0 vf = 3 + 0 vf = 3 m/s (t) (t) + vi + vi

  5. Practice Time • A car accelerates from a standstill to 60 km/s in 10 s. What is its acceleration? • A car accelerates from 25 mi/hr to 55 mi/hr in 0.0083 hr. What is its acceleration? • A runner has a velocity of 11.1 m/s for 9 seconds until he finishes the race and comes to a stop. What is his acceleration? • A motorcyclist has an acceleration of 5 mi/hr2. If his initial velocity is 45 mi/hr, what is his final velocity after 4 hours? Answer: a = 6 km/s2 Answer: a = 3,614.5 mi/hr2 Answer: a = -1.23 m/s2 Answer: vf = 65 mi/hr

  6. Graphing Acceleration Graphs can visually help us to understand an object’s motion. Remember… • Slope: the steepness of a line. • Calculated as rise = Δy run Δx • On a velocity vs. time graph, this means… • Calculated as rise = Δy = velocity run Δx time Therefore on a velocity vs. time graph, the slope= acceleration.

  7. Graphing Acceleration Describe the acceleration of the object in each graph. The object is moving at a constant speed, therefore it has 0 acceleration The object is not moving, therefore it has 0 acceleration The object is slowing down, therefore it has a negative acceleration The object is speeding up, therefore it has a positive acceleration

  8. Graphing Acceleration You can also describe the acceleration of an object by looking at distance vs. time graphs. The object is moving at a constant speed, therefore it has 0 acceleration The object is not moving, therefore it has 0 acceleration The object is slowing down, therefore it has a negative acceleration The object is speeding up, therefore it has a positive acceleration

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