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Free Fall


Lets take a feather and release it from a certain height it falls freely to the ground. Its not only a feather anything we release from a height reaches the earth. Why is it so?
Free Fall
Feather undergoing a free fall

Free fall is a pull a body experiences as gravity acts on it. It is what a sky diver, a swimmer or any thing experiences when given a push from a height. 

What is Free Fall?

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A Free fall is a pull what a body experiences in downward direction. It was Galileo to prove that all objects fall at the same rate whatever the mass be! At the beginning the fall has low speed and at the end it will be more. It tells about how long a body has been moving in downward direction and how far it moves.

Free Fall Speed

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A Free fall speed is that what decides it velocity and acceleration. Its acceleration will be constant through out whereas its velocity varies is based on air resistance. The Free fall speed depends on from what height a body is released.

The velocity depends on height, the more the height is, the greater is the speed of an object when it reaches the ground. It tells that some acceleration on objects under free fall and the same is known as 'free fall acceleration'.

Free Fall Acceleration

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Galileo using his famous inclined plane experiments discovered that acceleration of a free falling body is constant throughout. It does not change while the object is in free fall. The direction of this acceleration acts downward. Free fall acceleration depends on planets size and mass.

Lets see what will be the acceleration?
The free fall acceleration is that what a body experiences due to gravity. Weight is that a body experiences on an object. It is given by
F = W = mg
Hence the acceleration would be
a = $\frac{F}{m}$ = $\frac{W}{m}$ = $\frac{mg}{m}$
a = g
The acceleration of the body is equal to the gravity. The acceleration of object near surface of earth is 9.8 m/s2.

Free Fall Equations

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When a body is in a free fall. There are three equations of motion satisfying namely
h = $\frac{1}{2}$ gt2
v2 = 2gh
v = gt
Here v is the velocity of the body,
g is the acceleration due to gravity,
h is the height of the body,
t is the time taken.

Free Fall with Air Resistance

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Its a fact that any thing that thrown from a height falls towards the earth. Lets take a coin and a feather and throw it from a same height simultaneously. what falls faster and why?

You may wonder that even though the free fall is independent of mass! what makes some object fall on the earth sooner than the other?
There is something acting with the free fall known as air resistance. Air resistance is that a object experiences as a result of collisions of the surfaces with air molecules. It leads to decrease in speed of the object.

Free Fall Problems

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Here are given some problems based on free fall that might be helpful for you:

Solved Examples

Question 1: A stone is thrown from rest. What will be its velocity and distance traveled after 5 seconds?
Given: Time taken t = 5 s
Acceleration due to gravity g = 9.8 m/s2

The velocity of the stone from rest is v = gt = (9.8 m/s2) (5 s) = 49 m/s
The distance traveled is given by d = $\frac{1}{2}$ gt2 = $\frac{1}{2}$ $\times$ 9.8 m/s2 $\times$ (5 s)2 = 122.5 m.

Question 2: A ball is thrown from a 100 m building. How long it will take to hit the ground?
Given: Distance covered d = 100 m,
          Initial velocity vi = 0,
          Acceleration due to gravity a = g = 9.8 m/s2,
          Time taken t = ?
At rest distance traveled d = $\frac{1}{2}$ $\times$ a $\times$ t2
Time taken t = $\sqrt{\frac{2d}{a}}$
                   = $\sqrt{\frac{2 \times 100 m}{9.8 m/s^2}}$
                   = 4.51 s.