1. Gravity & Free Fall

2. Elephant vs. Feather
If both are dropped from the same height at the same time, which will hit the ground first?
On Earth?
On the moon?

3. Freefall Movement of an object towards earth solely because of gravity
Gravity acts downwards towards center of earth
Acceleration due to gravity for any falling object = g
g= 9.8 m/s2

4. What “g” means
Any object in free fall will increase its speed/velocity by 9.8 m/s each second.
g (9.8 m/s2) stays constant for the duration of free fall

5. Ball in free fall Time = 0 s v = 0 Time = 1 s v = 9.8 m/s
The change in ball’s speed
is always 9.8 m/s2
Time = 2 s
v = 19.6 m/s
ball is covering more distance
the longer it falls
Time = 3 s
v= 29.4 m/s

6. Viewing Free Fall
Free Fall applet

7. Air Resistance Present on earth acts in opposite direction of gravity
(reduces acceleration)
Falling Ball
Gravity
g=9.8m/s2
Air resistance

8. Air Resistance If objects fall for long period of time:
Force of Air resistance = force of gravity
Forces balanced
Object falls at constant speed called terminal velocity

9. Terminal Velocity Air resistance increases with: 1. Increasing Speed
2. Increasing surface area
Parachutes slow
downward acceleration

10. Viewing Terminal Velocity

11. Elephant vs. Feather Without air resistance (outer space)
Free falling objects
Both hit at same time

12. Elephant vs. Feather With air resistance (earth) With air resistance
Elephant hits first