Free Fall Acceleration due to Gravity

Free Fall l What causes things to fall? l How fast do things fall? l How far do things fall in a given time?

What makes things fall? GRAVITY!

l Gravity is an acceleration

Gravitational Acceleration l All objects with mass are attracted to all other objects with mass. mutual l Technically, this is a mutual attraction. l BUT, since the mass of the Earth is so much larger, objects “fall” toward the Earth.

How fast do objects fall? l All objects fall toward the Earth at the same rate… 9.8 m/sec each sec 9.8 m/sec 2

Falling... l That means, an object gains 9.8 m/sec of speed each second it falls! t l So if we drop an object, we can find the instantaneous speed after t seconds. v = 9.8 m/sec 2 ( t sec)

So… l How fast are you moving if you jump from the water tower and fall for 10 sec? v = 9.8 m/sec 2 ( 10 sec) v = 98 m/sec

How far do things fall in a given time? In one second an object will fall 5 m –started at 0 m/s and ended at 9.8 m/s at the end of 1 second which averages to 4.9 m/s. Remember distance is the product of average speed and time.

How far do things fall in a given time? 5 ( t 2 ) Finding the distance an object falls distance = half of gravity x time squared d = 1/2 g t 2 d = 4.9 m/sec 2 ( t 2 ) distance fallen is about 5 ( t 2 )

So... l How far have you fallen 10 seconds after you jump off the water tower? d = 4.9 m/sec 2 ( 10 sec) 2 d = 490 m

l Now consider an object thrown straight up l At the highest point, when the object is changing direction, its instantaneous speed is zero

l During the up motion, the object slows to zero and then picks up speed coming down l The instantaneous speed at points of equal elevation in the path, is the same whether the object is moving up or down l Their velocities are different because they have different direction

Air Resistance l Drop a feather and a coin and we notice the coin reaches the floor first l Air resistance is responsible for these different accelerations l When the air is removed from a tube, the feather and a coin fall side by side with the same acceleration