I. Acceleration due to GravityA. Special case of Uniform Acceleration

1) Constant force acting on an object imparts uniform acceleration2) Gravity is a constant force3) 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/s2

C. Air Resistance1) Which hits first, brick or a feather?2) g is constant for all things; weight of the object doesn’t matter3) Shape of a feather and its light weight do cause it to interact with the air

strongly = air resistancea) Large surface areab) Small weight

4) In a vacuum (no air) all things fall at the same rate(on Earth)

24cm/s0.05s1.2cm

tdv

graph velocity of slope

xy

tva

y

x

22 9.8m/s

s980cm

0.40s392cm/s

0.05s0.4572cm/s464

ΔxΔy

ΔtΔva

II. Tracking Falling ObjectsA. Ball dropped from a building

1) Find velocity and distance at 0.5-2 s2) Plot distance vs. time

v = vo + atd = vot + ½ at2

B. Throwing a ball straight down1) Now we have an initial velocity v0

2) Acceleration due to gravity is still g = 9.8 m/s2

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 up1) Direction of velocity and acceleration are very important

2) What is the accelerationat the top of the trajectory?What is the velocity?

20 2

1 tatvd

tavv 0

+ v

- v

- a- a

3) Example: sample exercise 3.2