Lecture 6
Freely Falling Objects
1
Freely Falling Objects
Near the earth’s surface, the acceleration due to gravity g is constant:
g = aEarth’s surface = 9.81 m/s2 toward the center of the earth
A freely falling object:
•is an object that moves under the influence of gravity only.
(Neglecting air resistance.)
•An object is in free fall as soon as it is released,
whether it is dropped from rest, thrown downward, or thrown upward
Question:
What about the mass of an object?
Answer:
The acceleration of gravity is the same for all objects near
the surface of the Earth, regardless of mass.
Dr. Loai Afana
2
Free.Fall - an Object Dropped




Initial velocity is zero (v0=0)
Frame: let up be positive
Use the kinematic equations
Generally use y instead of x since
vertical
y
x
vo= 0
a=g
1 2
y  at
2
a  9.8 m s 2
use y instead of x
Up Y the positive
3
Dr. Loai Afana
Free. Fall - an Object Thrown Downward
With upward (Y) being positive : acceleration will be negative,
y
a= g = -9.8 m/s²
-Initial velocity V0  0
initial velocity will be negative!!
x
With downward (Y) being positive : acceleration will be positive,
Dr. Loai Afana
4
Free.Fall - object thrown upward
 Initial velocity is upward, so
positive .
v=0
 The instantaneous velocity at the
maximum height is zero. (because
object stopped)
y
 a = g everywhere in the motion
(g) is always downward, negative
g = -9.8 m/s²
x
Dr. Loai Afana
5
Thrown upward
 The motion may be symmetrical
- then tup = tdown
- then vf = -vo
 The motion may be not symmetrical
- Break the motion into various parts
- generally up and down
Dr. Loai Afana
6
Non-symmetrical
Free Fall
 Need to divide the
motion into segments
Possibilities include:
 Upward and downward
portions
 The symmetrical portion
back to the release point
and then the nonsymmetrical portion
Dr. Loai Afana
7