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Newton's Third Law dictates every action has an opposite and equal reaction. In other terms, if Object A exerts a force on Object B, Object B will exert the same amount of force back onto Object A.
Rocket propulsion utilizes this concept to boost the rocket upwards-- by pushing itself against the ground with highly pressurized gas (or water, in terms of liquid propulsion), the ground, in turn, pushes against the rocket with an equal and opposite force, thus lifting it off the ground. Using this law, we are able to decipher two important factors when launching: the mass of the rocket and the force it applies on the ground-- for the initial launch to occur, the propulsion system must be capable of creating a downward force greater than the rocket's mass multiplied by the gravitational acceleration (9.81 m/s). [ Frocket > m*g ]
Conservation of Momentum
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The left-hand side describes the initial momentum of two objects, [ Note: momentum(p) = mass(m) * velocity(v) ] and the right-hand side describes the final momentum.
Applying this to rocket propulsion, visualize the two objects being the rocket and the propellant inside the rocket. When the propellant burns, it becomes tiny particles of pressurized gas shot out of the back of the rocket.
If the rocket is initially at rest, when this occurs, the rocket's momentum will compensate for that downward velocity by pushing itself upwards as a result, allowing the rocket to maintain flight for a longer period of time. To improve the rocket's trajectory, we must consider the velocity of the gas as it exits the rocket and the amount of propellant in the rocket.
Components of a Solid Propulsion System
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