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Free Fall: How Fast An apple falls from a tree. Does it accelerate while falling? Yes (ex. Falling 2 m vs 100 m) What makes it accelerate????? Gravity!!!

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Free Fall: How Fast We will ignore air resistance right now. If gravity is the only thing affecting the falling object, we say it is in Free Fall.

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Free Fall Speeds of Objects Dropped from Rest Elapsed Time(s)Instantaneous Speed(m/s) 00 1 9.8 2 19.6 3 29.4 4 39.2 5 49 t 9.8t Note: Elapsed time is the time that has passed since the beginning of the fall

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Free Fall: How Fast Notice that during each second of fall, the speed of the object increases by 9.8 m/s This gain in speed is the acceleration a = Change in velocity = 9.8m/s = 9.8m/s 2 time interval 1 s

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Question If a ball were dropped from rest, how fast would it be traveling after 1 second? 9.8 m/s

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Free Fall: How Fast Because the object’s acceleration is due to gravity, we use the letter g to represent the acceleration. SO………………………. Instantaneous speed = acceleration x elapsed time

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Free Fall: How Fast Instantaneous speed = acceleration x elapsed time This can be represented in an equation format: v=gt where v is velocity or speed, g is 9.8m/s 2, and t is elapsed time

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Question If a rock was dropped from rest, what would the speed be at 4.5 seconds? v = gt, v = 9.8 x 4.5, v = 44.1 m/s What about at 8 seconds? 78.4 m/s What about at 15 seconds? 147 m/s

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Free Fall: How Fast Now let’s think about an object that is thrown into the air, and then falls back down. While going up… it slows down at 9.8 m/s 2 At the top….it’s velocity is 0 m/s While falling…it’s just like before, it increases it’s speed by 9.8m/s each second.

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Free Fall: How Far How fast something moves is different from how far. Elapsed Time(s)Instantaneous Speed(m/s) 00 1 9.8 2 19.6 3 29.4 4 39.2 5 49 t 9.8t

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Free Fall: How Far Just because the object increases it’s speed by 9.8 m/s in the first second, doesn’t mean it traveled 9.8 meters. It started from rest, so we have to find it’s average speed over the 1 second. It’s initial speed was 0m/s and it’s final at one second was 9.8 m/s. Average Speed = 0 + 9.8 = 4.9 m/s 2 SO….. It’s distance was 4.9 meters in 1 second.

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Free Fall: How Far So there is an equation to calculate the distance traveled for any accelerating object (free falling or not). d = 1 at 2 2

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