#

##

##
SUDESHNA PAUL
EDUCATIONAL COMPANION

Free
Fall
Aeroplane
Rocket
Back to Physics

If you do not find the animation below download & install Java Runtime to update your computer

Suppose two objects, one light ,another heavy are dropped
off a very tall building from the same height at the same time. Which
objects - will hit the ground first ?

Suppose also that air resistance could be eliminated such that
none would experience any air drag during the course of their fall. Which object
- will hit the ground first

An object that **falls through a vacuum** is subjected to only one
external force, the gravitational force, expressed as the weight of the object.
The weight equation defines the weight **W** to be equal to the mass of the
object **m** times the gravitational acceleration **g **

W = m * g

the
value of **g** is 9.8 meters per square second on the surface of the earth.
The gravitational acceleration **g** decreases with the square of the
distance from the center of the earth. But for many practical problems, we can
assume this factor to be a constant. An object that moves because of the action
of gravity alone is said to be **free falling**. If the object falls through
the atmosphere, there is an additional drag force acting on the object.
The motion of any moving object is described by Newton's second law of
motion, force **F** equals mass **m** times acceleration **a**:
F = m * a
and
a = F / m
For a free falling object, the **net external force** is
just the weight of the object:

F = W
so
a = W / m = (m * g) / m = g

The **acceleration** of the object equals the
gravitational acceleration. The mass, size, and shape of the object are not a
factor in describing the motion of the object. So all objects, regardless of
size or shape or weight, free fall with the same acceleration. In a vacuum, a
beach ball falls at the same rate as an airliner. The remarkable observation
that all free falling objects fall with the same acceleration was first proposed
by **Galileo,** nearly 400 years ago.

When the airplane moves forward , due to air viscosity, circulation of air takes place. Now
the upper surface of the wing is made more curved than the lower one. The air
over the upper wing surface has to cover more distance , compared to that of lower
one during the same interval of time. So the
wind velocity on the upper surface is higher and so the velocity head. According to the
Bernoulli's theorem

**(pressure head) + (velocity
head) + (gravitational head)= (constant)**

** P**_{u} + (1/2)pv^{2}_{u}
+ pgh =P_{l} + (1/2)pv^{2}_{l} + pgh

where**
**P= air pressure, suffix u stands for upper, l stands for lower, p=air or
fluid density , g =gravity , v= velocity of air, h=height

the sum of gravitational head ,pressure head and velocity head
always remains constant. As the velocity head increases on the upper side, its
pressure head decreases. The
pressure on the upper surface will be less than the lower side. This difference of pressure between the upper and lower
produces thrust which causes the lift.

###