Chapter 3 Lecture 1 Falling Objects. Acceleration due to Gravity Special case of Uniform Acceleration Constant force acting on an object imparts uniform acceleration Gravity is a constant force Any dropped object accelerates uniformly Measuring the Acceleration due to Gravity.
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Chapter 3 Lecture 1 Falling Objects • Acceleration due to Gravity • Special case of Uniform Acceleration • Constant force acting on an object imparts uniform acceleration • Gravity is a constant force • Any dropped object accelerates uniformly • Measuring the Acceleration due to Gravity v = d/t =1.2cm/0.05s = 24cm/s v = d/t =16cm/0.05s = 320cm/s
Dy • Compute average velocity for each time period • Plot velocity versus time • Remember • Compute acceleration due to gravity: g = 9.8 m/s2 • Air Resistance • Which hits first, brick or a feather? • g is constant for all things; weight of the object doesn’t matter • Shape of a feather and its light weight do cause it to interact with the air strongly = air resistance • Large surface area • Small weight • In a vacuum (no air) all things fall at the same rate (on Earth) Dx
v = vo + at d = vot + ½ at2 • Tracking Falling Objects • Ball dropped from a building • Find velocity and distance at 0.5-2 s • Plot distance vs. time
Throwing a ball straight down • Now we have an initial velocity v0 • Acceleration due to gravity is still g = 9.8 m/s2 • Ball is thrown down at 20 m/s. What are the velocities and distances at 1 and 2 seconds? • Throwing a ball straight up • Direction of velocity and acceleration are very important • What is the acceleration at the top of the trajectory? What is the velocity? - a - a + v - v