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As a rocket flies through the air, it both translates and rotates .The rotation occurs about a point called the CENTER OF GRAVITY.. The center of gravity is the average location of the weight of the rocket. The mass and weight are distributed throughout the rocket, and for some problems, it is important to know the distribution. But for rocket trajectory and maneuvering we need to be concerned with only the total weight and the location of the center of gravity.

A restoring force exists for this model rocket because the center of pressure is below the center of gravity. If the center of pressure is above the center of gravity, the lift and drag forces maintain their directions but the direction of the torque generated by the forces is reversed. This is called a de-stabilizing force small displacement of the nose generates forces that cause the displacement to increase. The conditions for a stable rocket are that the center of pressure must be located below the center of gravity.

There is a relatively simple test that you can use on a model rocket to determine the stability. Tie a string around the body tube at the location of the center of gravity. Be sure to have the parachute and the engine installed. Then swing the rocket in a circle around you while holding the other end of the string. After a few revolutions, if the nose points in the direction of the rotation, the rocket is stable and the center of pressure is below the center of gravity. If the rocket wobbles, or the tail points in the direction of rotation, the rocket is unstable. You can increase the stability by lowering the center of pressure, increasing the fin area, for example, or by raising the center of gravity, adding weight to the nose.

The Four Forces of Flight

An aircraft in straight and level flight is acted upon by four forces:

Lift- The upward force that that is created by the movement of air above and below a wing. Gravity- The force that pulls all objects towards the Earth. Thrust- The force that moves a plane foward through the air. Thrust is created by a propeller or a jet engine. Drag- The air resistance that tends to slow the foward movement of an airplaine

The opposing forces balance each other; lift equals gravity and thrust equals drag. Any inequality between thrust and drag, while maintaining straight and level flight, will reslt in acceleration or deceleration until the two forces again become balanced.

__Newtons Laws of Motion__
 * 1st Law-** The first law - sometimes referred to as the law of inertia - states that if the forces acting upon an object are balanced, then the acceleration of that object will be 0.


 * 2nd Law-** The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.


 * 3rd Law-** Every action has an equal or opposite reaction.