1. Chapter 13, Section 2 Gravity and Motion
Part 1

2. Falling Objects
Galileo - all objects fall to the ground at the same rate (9.8 m/s/s) because the acceleration due to gravity is the same for all objects.
Velocity of falling objects: ∆v = g x t g = 9.8 m/s/s t=falling time

3. Example
1. If a stone at rest is dropped from a cliff and it takes 3 seconds to hit the ground, what is the stone’s downward velocity when it hits the ground?
∆v = g x t
∆v = 9.8 m/s/s x 3s
∆v = 29.4 m/s

4. Practice
A penny at rest is dropped from the top of a stairwell. What is the penny’s velocity when it hits the ground after falling for 4.5 seconds?
∆v = g x t
∆v = 9.8 m/s/s x 4.5 s
∆v = 44.1 m/s

5. Air Resistance
Air resistance is a type of fluid friction that opposes the motion of objects moving through the air.
The amount of air resistance on an object depends on its size and shape.

6. Terminal Velocity
Eventually the gravitational force pulling down on a falling object equals the force of air resistance pushing up.

7. The forces are then balanced, the object quits accelerating and falls at a constant velocity = terminal velocity.

8. Free Fall
An object is in free fall only if gravity is pulling it down and no other forces are acting on it.
Free fall can only happen in a vacuum or in space.