Rocket Motors Energetics Exothermic Reactions Forces Inspire a

Rocket Motors Energetics, Exothermic Reactions & Forces “Inspire a generation”

How does the rocket motor work? The Race For The Line competition rocket is filled with a solid propellant. This makes it a solid fuel rocket motor. The propellant is a mixture of the solid fuel and the solid oxidiser. The oxidiser provides the oxygen needed for the fuel to burn. Other types of rocket: A liquid fuel rocket uses a liquid fuel and a liquid oxidiser. In the Saturn 5 moon rockets, these were liquid hydrogen and liquid oxygen. * Not present in a ‘ 0’ motor A hybrid rocket (such as the Bloodhound SSC rocket motor) uses a solid fuel and a liquid oxidiser (Hydrogen Peroxide).

How does the rocket motor work? When the rocket is ignited, the fast exothermic chemical reaction (combustion) of the solid fuel and oxidiser produces lots of hot gas molecules. The hot gases produced expand rapidly and push against the inside of the rocket motor creating pressure. The only way for the hot, expanding gases to escape, is through the small clay nozzle at the back of the motor. It is the ejection of these rapidly expanding hot gases at high speed from the rocket nozzle that creates the thrust. Energy is released as heat as the oxygen in the oxidiser reacts with the fuel and new molecular bonds are made. A chemical reaction that gives out heat is called an exothermic reaction. In a rocket, this reaction happens very quickly. A small volume of the solid propellant quickly becomes a large volume of hot gases.

The motor used in the Race For The Line model rocket cars is an ESTES B 6 -0 solid fuel rocket. The B indicates that it has twice as much power as an A class rocket. The number ‘ 6’ is the motor’s average thrust in Newtons. The number ‘ 0’ is the delay in seconds between end of thrust and the ejection charge that is often used to deploy a parachute in a flying rocket design. Potassium Nitrate, Charcoal and Sulphur are combined to create the ‘black powder’ propellant in small rocket motors and fireworks. This is one of the earliest types of rocket power and was developed in China in the 13 th Century The Potassium Nitrate provides the Oxygen (oxidiser) and the Carbon in the charcoal is the fuel. The Sulphur lowers the temperature needed to start the reaction.

The graph opposite shows the thrust of the competition motor over time. Can you answer these questions: • What measure is used for thrust? • What is the peak thrust? • How long does it take for the motor to reach peak thrust? • How long does the reaction in the motor last?