Concept 2 Notes - Acceleration.pdf

 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....

 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 vf - v i up a= – Negative acceleration: when an t object slows down. vf = final velocity vi = initial velocity  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 a = (45 – 35) vf = 45 km/hr 0.25 t = 0.25 hr a = 10. a=? 0.25 a = v f - vi a = 40 km/hr2 t  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 a = (0 – 80) vf = 0 m/s 10 The negative t = 10 s acceleration a = -80. a=? makes sense 10 because the jet 2 is slowing down a = v f - vi a = -8 m/s as it comes to a t stop.  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 vf = at + vi vi = 0 m/s vf = (1.5)(2) + 0 t=2s vf = ? vf = 3 + 0 (t)a = vf - vi (t) vf = 3 m/s t at = vf – vi + vi + vi at + vi = vf  Practice Time 1. A car accelerates from a standstill to 60 km/s in 10 s. What is its acceleration? Answer: a = 6 km/s2 2. A car accelerates from 25 mi/hr to 55 mi/hr in 0.0083 hr. What is its acceleration? Answer: a = 3,614.5 mi/hr2 3. 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? Answer: a = -1.23 m/s2 4. 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: v = 65 mi/hr f  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. Graphing Acceleration Describe the acceleration of the object in each graph. The object is The object is moving at a not moving, constant therefore it speed, has 0 therefore it acceleration has 0 acceleration The object is The object is slowing speeding up, down, therefore it therefore it has a has a positive negative acceleration acceleration  Graphing Acceleration You can also describe the acceleration of an object by looking at distance vs. time graphs. The object is The object is not moving, moving at a therefore it constant has 0 speed, acceleration therefore it has 0 acceleration The object is The object is slowing speeding up, down, therefore it therefore it has a has a positive negative acceleration acceleration