Presentation on theme: "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!!!"— Presentation transcript:
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!!!
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.
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
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
Question If a ball were dropped from rest, how fast would it be traveling after 1 second? 9.8 m/s
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
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
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
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.
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
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.
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