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Gravity is a well-known term and everyone in general knows that it is a pulling force. It is such a force which keeps everything in contact and everything thus constrained to something. Gravity of earth keeps the moon where it is supposed to be and gravity keeps you where you are now. If you weren’t under gravity of earth, you would be floating in space. This understanding of gravity is not really limited to the force of attraction between two masses or let’s says a pulling force. It is something more mysterious.

The mystery of gravity has kept a lots and lots of scientists till the date intact to think about it. Starting from medieval ages and still now, people are studying gravity to find what exactly it is. The big two names that come automatically on our mind with this word are Newton and Einstein. Newton started by calculating the forces and gave us relationships on the amount of gravitational force between masses on space. However, he was incomplete and until Einstein no one had really figured out what really gravity is and how does it work in nature.

Newton’s Gravity:
When an apple fell from a tree in Newton’s garden, he described gravity to be a pulling force. He said that there is a force of attraction between two masses. This force is a function of (depends upon) the mass of the objects and the distance between them. Newton’s law of gravity is given as:
Gravitational force = (G * m1 * m2) / (d2)
where G is the gravitational constant, m1 and m2 are the masses of the two objects, and d is the distance between the centres of gravity of the two masses.

Einstein’s Gravity:

The understanding of gravity was understood by the scientists and people as described by Newton in 1680’s. But this was until 1900’s when Einstein found out the gravity to be working in a different way. Newton was wrong with the sense how actually the gravity works. Einstein calls a gravity not to be a force at all. It is rather a space-time distortion; it is a curve in space.

Space-time: Space is the three dimensional representation of everything we observe and everything that occurs. It is the space that allows us to move us freely in three dimensions – up/down, left/right, forward/backward. Time is in our sense a tool to measure the happenings and events. Besides this, time is somewhat more sophisticated tool which is woven with the space (location/position). Having one without the other has no meaning in physical world.
An example: If there was no space, you wouldn’t exist; you wouldn’t be able to move (no degrees of freedom, left-right, up-down ..... ) In this case, you can’t talk about time, if you can’t move, if you can make any events. Thus without space, any time wouldn’t exist and vice-versa.
Thus, space-time is a common quantity and as time and space are bonded together.
Space is a fibre where our universe exists. This can be seen on the picture below.

Thus, when an object is placed on this fabric space, it distorts the space-time and created a curve on the space-time. This is what we experience: gravity. Big masses create big distortion (big curvatures) while small objects create, small distortion. This is because of this face that the smaller objects are pulled towards bigger objects. Consider this with earth and moon.
Our earth being a big mass has created distortion in space-time and thus a curvature is created on the fabric of space. The moon is thus constrained to move in its orbit and hence attracted towards the earth and so are we all. 

Sun is even a huge star compared to our earth. It thus creates even bigger curvature in space-time and earth as well as other big planets laying in its gravitation field (area upto its curvature effect) are attracted to it and hence revolve around the sun.

In our 3-dimensional world, an aircraft has three degrees of freedom.  It is very important to make an overview of these three degrees of freedom to understand the stability and control of an aircraft. An aircraft rotates about its center of gravity (c.g). The center of gravity of any object is a point in the middle of the mass where the mass is balanced.  It can be seen from the following examples:

The mass on each of the sides of these objects is equal. In other words, he object is in equilibrium when the object is supported at the point of cg.


Aircraft Roll Motion:
A roll motion is an up and down movement of the wings of the aircraft as shown in the picture hereby. This type of motion is used to change the direction of an aircraft during flight. For an aircraft to be rolled, ailerons’ are used at the rear section of the wings. The movement of ailerons cause the aircraft to roll.  


 Aircraft Pitching Motion:
A pitch motion is an up or down movement of the nose of the fuselage of the aircraft as shown in the picture hereby. This type of motion is used to change the altitude of an aircraft during flight. For an aircraft to be pitched, elevators are used at the rear section of the horizontal stabilizer. The movement of elevators up or down cause the aircraft to pitch.


Aircraft Yawing Motion:
A yaw motion is a side to side movement of the nose of an aircraft during flight. This can be seen clearly in the picture below. This type is motion is vital for changing the direction or rotating the aircraft. Rudders located at the vertical stabilizers are used for yawing motions in an aircraft.


In the end, I wish you a happy new year on the occassion of new year 2010.

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