I.Acceleration due to Gravity A.Special case of Uniform Acceleration 1)Constant force acting on an object imparts uniform acceleration 2)Gravity is a constant force 3)Any dropped object accelerates uniformly B.Measuring the Acceleration due to Gravity Chapter 3 Lecture 1 Falling Objects v = d/t =1.2cm/0.05s = 24cm/s v = d/t =16cm/0.05s = 320cm/s

1)Compute average velocity for each time period 2)Plot velocity versus time 3)Remember 4)Compute acceleration due to gravity: g = 9.8 m/s 2 C.Air Resistance 1)Which hits first, brick or a feather? 2)g is constant for all things; weight of the object doesn’t matter 3)Shape of a feather and its light weight do cause it to interact with the air strongly = air resistance a)Large surface area b)Small weight 4)In a vacuum (no air) all things fall at the same rate (on Earth) yy xx

II.Tracking Falling Objects A.Ball dropped from a building 1)Find velocity and distance at s 2)Plot distance vs. time v = v o + at d = v o t + ½ at 2

B.Throwing a ball straight down 1)Now we have an initial velocity v 0 2)Acceleration due to gravity is still g = 9.8 m/s 2 3) 4) 5)Ball is thrown down at 20 m/s. What are the velocities and distances at 1 and 2 seconds? C.Throwing a ball straight up 1)Direction of velocity and acceleration are very important 2)What is the acceleration at the top of the trajectory? What is the velocity? + v - v - a

3)Example: sample exercise 3.2