Free Fall Notes

Free Fall Introduction A free-falling object is an object which is falling under the sole influence of gravity. Two important motion characteristics which are true of free-falling objects: Free-falling objects do not encounter air resistance All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s 2 (often approximated as 10 m/s 2 ) We use the symbol g to denote free fall acceleration.

Direction Matters!  We need to denote the up and down direction  We are going to use + for up and – for down  The + and – are just to identify direction, they have nothing to do with the magnitude So our acceleration for free fall will always be -9.8 m/s 2

Sample Problem 1 Audrey drops a ball from the top of a 25 m tall ladder. a. How fast will the ball be traveling just before it hits the ground?

Write down the known variables and what you are looking for. v 0 = 0 m/s d = -25 m (remember down direction = -) a = -10m/s 2 v f = ? Determine which equation to use v f 2 = v ad v f = √(0m/s + (2(-10m/s 2 )(-25m)) = m/s (choose the – component of the square because of the direction) So the ball will be traveling 22.4 m/s in the downward direction

b. How long will it take for the ball to hit the ground? Write down the known variables and what you are looking for. v 0 = 0 m/s d = -25 m a = -10m/s 2 v f = m/s (from part a) Determine which equation to use d = v 0 t+ ½at 2, v 0 = 0 m/s so d = ½at 2 t = √(2d/a)= √[(2 x -25 m)/ (-10 m/s 2 )] = 2.2 sec

Sample Problem 2 Trevor tossed a ball up with a velocity of 15 m/s. a. How high will the ball rise?

Write down the known variables and what you are looking for. v 0 = 15 m/s v f = 0 m/s a = -10m/s 2 Determine which equation to use v f 2 = v ad d = (v f 2 - v 0 2 ) /2a d = [(0 m/s) 2 – (15 m/s) 2 ] / (2 x -10 m/s 2 ) = m So the ball will go up m

The Big Misconception Doesn't a more massive object accelerate at a greater rate than a less massive object? Wouldn't an elephant free-fall faster than a mouse? Free-fall is the motion of objects which move under the sole influence of gravity; free-falling objects do not encounter air resistance. More massive objects will only fall faster if there is an appreciable amount of air resistance present.