Scientific Explanation

Rockets contain some of the most common physics principles such as Newton's laws of motion. Rockets may seem interesting and cool, but the science behind them is even more fascinating. Read the document attached below to learn about the science behind these amazing devices.

Scientific Explanation

Rockets display the Principia, Newton’s three laws of motion. These three laws state:

1. Objects at rest will stay at rest and objects in motion will stay in motion in a straight line unless acted upon by an unbalanced force.

2. Force is equal to mass times acceleration.

3. For every action, there is always an opposite and equal reaction.

Newton’s first law of motion:

In rocket flight, forces often become balanced and unbalanced. Before the rocket is launched, it is in a balanced state, as it is placed on the launch pad. When the rocket is launched, the pressure pushes the rocket upwards while gravity pulls it back down. The rocket becomes unbalanced due to the thrust performed by the rocket when the engines are ignited. The rocket keeps traveling upward with a decreasing speed as the fuel runs out. It eventually stops at the highest point (where v=0 m/s) and falls back to earth with an increasing speed. Objects in space also react to forces. A spacecraft or satellite in space at a constant speed will continue to move in a straight line unless an external force is acted upon it. This only happens when the object is far away from Earth. When it is close at a relative distance from Earth, Earth’s gravitational force will act upon it, causing the object to move in a circular motion around Earth.

Newton’s second law of motion:

The general equation F=ma is used in this law. The force (F) is the pressure that is created by the explosion within the engine. This is what shoots the gas o0en way, and the actual rocket body the other. Unlike other objects, the mass of rockets changes during its flight. The mass is a combined value of all the parts, including the engines, payload, and propellants. This amount is constantly changing as the engines are ignited. This causes an unbalanced equation (F=ma). In order to keep it balanced, the acceleration of the rocket must increase as the mass decreases. This explains why rockets start off my moving slowly and start moving faster as they progress into space.

Newton’s third law of motion:

A rocket is only able to launch when it expels gas from its engine. This is because as the weight of the rocket pushes on the gas, the gas’s thrust pushes on the rocket, causing it to move upward.

A model rocket’s motor depends on impulse to exert the amount of force needed for the rocket to take off. Impulse can also be used to define the fast-acting force the motor has on the model rocket. The model rocket demonstrates Newton’s second law of motion, as the rocket’s upward acceleration produced by the motor’s force is directly proportional to the magnitude of the rocket’s net force. The rocket’s acceleration is also in the same direction as the net force and is indirectly proportional to the mass of the rocket.

To determine the model rocket’s motor’s total impulse and propellant specific impulse, we will use a thrust-time curve with data from static testing. A typical thrust-time curve is shown below:

Total impulse is the integral of the thrust (force) multiplied the duration of the motor’s thrust (time), and the integral is the area under the curve.