Forces on a Rocket

9868cc7cfe4e26bc2ca68be692d6053d.jpg

Lift

Drag

thrusters-png.png

Thrust

Weight

Spacecrafts or flying Rockets are affected by the following :

  1. Thrust produced by the rocket engine.

  2. Force of Gravity from the celestial bodies.

  3. Air Drag if the rocket is moving through the atmosphere.

  4. Lift, which is usually very small.

By studying Rockets we can understand the fundamentals of forces and the object's response to the external force. The motion of an object as a response to the external force was first described by Sir Isaac Newton using the three laws of motion. 
Forces are vector quantities. A vector is the one which has both magnitude and a direction. When describing the action of forces, one must consider both magnitude and direction. During the flight, a rocket is always subjected to four forces; weight, thrust, and the aerodynamic forces, lift and drag. The magnitude of the weight depends on the mass of all of the parts of the rocket. The weight force is always directed towards the center of the earth and acts through the center of gravity. The black dot on the figure is the center of gravity on the Rocket body.

The magnitude of the Rocket thrust depends on the mass flow rate through the engine and the velocity and pressure at the exit of the nozzle. The thrust force normally acts along the longitudinal axis of the rocket and therefore acts through the center of gravity. Some full scale rockets can move, or gimbal, their nozzles to produce a force which is not aligned with the center of gravity. The resulting torque about the center of gravity can be used to maneuver the rocket. The magnitude of the aerodynamic forces involved depends on the shape, size, and velocity of the rocket and also on properties of the atmosphere. The aerodynamic forces act through the center of pressure, the orange dot on the figure. Aerodynamic forces plays an important rule for model rockets, but it might not be important for a full scale rocket, depending on the mission of the rocket. Full scale boosters usually spend only a short amount of time in the atmosphere, which are later released to the outer space.

In the Rockets, the magnitude and sometimes even the direction of the four forces is constantly changing. If we carefully add up all the forces considering the magnitude and direction, if obtain a net resultant force( F net ) on the Rocket body. It is described by the Newton's laws of motion.

The magnitude of the Rocket thrust depends on the mass flow rate through the engine and the velocity and pressure at the exit of the nozzle. The thrust force normally acts along the longitudinal axis of the rocket and therefore acts through the center of gravity. Some full-scale rockets can move, or gimbal, their nozzles to produce a force which is not aligned with the center of gravity. The resulting torque about the center of gravity can be used to maneuver the rocket. The magnitude of the aerodynamic forces involved depends on the shape, size, and velocity of the rocket and also on properties of the atmosphere. The aerodynamic forces act through the center of pressure, the orange dot on the figure. Aerodynamic forces plays an important rule for model rockets, but it might not be important for a full scale rocket, depending on the mission of the rocket. Full scale boosters usually spend only a short amount of time in the atmosphere, which are later released to the outer space.

Source Credits : NASA