Acceleration due to gravity

1
Unit 2-6

• Acceleration due to gravity

2
Free Fall

• If two objects are dropped from the same height
  they should reach the ground at the same time.
• This is because they are both accelerated by the
  force of gravity.
• The acceleration due to gravity is 9.8 m/s2
  (usually rounded to 10 m/s2)
• Galileos Experiment

3
Air Resistance

• An elephant and a mouse would reach the ground at
  the same time, if there was no air resistance.
• The surface area to weight ratio of the mouse is
  greater than that of the elephant so the air
  resistance is higher.
• As the speed increases the air resistance
  increases and the object reaches TERMINAL
  VELOCITY.

4
Terminal velocity
Force of Air Resistance
5
Using Kinematic Equations

• 1. Calculate the distance traveled by a chipmunk
  falling out of an airplane for 4 seconds without
  a parachute.
• 2. What will be its velocity after 4 seconds?
• sut ½ at2 0 ½ x 10 x 42 80m
• vu at 10 x 4 40 m/s

6
Equations using acceleration due to gravity

• Assuming no air resistance how long would it take
  for an elephant and a feather to fall from the
  top of the school building (30 meters)?
  Acceleration due to gravity g 10 m/s2
• Use equation s ut ½ at2
• s is 30 m , u is 0 m/s and a is 10 m/s2
• Rearrange the equation to make t the subject
• t ?(2s/a)
• t ?(2 x 30/10) ?6