Free fall is the motion of an object under the influence of gravitational force only. During free fall, the acceleration due to gravity (g) is about 9.8 m/s2, causing the object's speed to increase by 9.8 m/s every second and its position to change according to the kinematic equations of motion. In a vacuum, where there is no air resistance, all objects in free fall accelerate at the same rate due to gravity regardless of their mass or shape.

1. FREE FALL

2. Free fall is the motion of an
object under the effect of
gravitational force only.
Free fall

3. Motion of bungee jumper Motion of skydivers

4. Important note
• Free fall does not mean that the object
is falling down only.
• Objects thrown upward or downward and
those released from rest are all the
examples of free fall.

5. Falling objects & air resistance
More air resistance on without
crumpled-up piece of paper
Less air resistance on
crumpled-up piece of paper

6. Falling objects & air resistance
In vacuum both feather and apple
falls at the same rate.
Reason:
In vacuum there is no air, it means
there is no air resistance.
So surface area and mass makes
no difference.

7. Acceleration due to gravity
0 s, v1 = 0 m/s
1 s, v2 = 9.8 m/s
2 s, v3 = 19.6 m/s
3 s, v4 = 29.4 m/s
4 s, v5 = 39.2 m/s
• During each second of fall, the speed
of a ball changes by 9.8 m/s.
• The change in speed is due to gravity.
• Hence, the acceleration in this case is
called acceleration due to gravity.
𝑔 = 9.8 m/s2

8. Sign convention
Position Velocity Acceleration
y > 0
y < 0
0 0
y y y y
v > 0 v < 0
a = -g
y

9. Equations of motion for free fall
Kinematical equations of motion is also applicable for free fall
because, free fall is an example of uniformly accelerated motion.
HORIZONTAL MOTION FREE FALL
vf = vi + at vf = vi − 𝑔t
xf − xi = vit +
1
2
at2
yf − yi = vit −
1
2
𝑔t2
vf
2
= vi
2
+ 2a(xf − xi) vf
2
= vi
2
− 2𝑔(yf − yi)

10. Position-time graph for free fall
Time (s) Position (m)
0 0
1 -4.9
2 -19.6
3 -44.1
4 -78.4
5 -122.5
1 2 3 4 5 6
t0
-40
-20
-60
y
-100
-80
-120

11. Velocity-time graph for free fall
Time (s) Velocity (m/s)
0 0
1 -9.8
2 -19.6
3 -29.4
4 -39.2
5 -49
1 2 3 4 5 6
t0
-20
-10
-30
v
-50
-40
-60

12. Acceleration-time graph for free fall
Time (s)
Acceleration
(m/s 𝟐
)
0 -9.8
1 -9.8
2 -9.8
3 -9.8
4 -9.8
5 -9.8
1 2 3 4 5 6
t0
-4
-2
a
-6
-8
-10
-12

13. Thank
you