UNDERSTANDING THE BASICS Rocket engines are different from car engines and steam engines, which produce rotary motion to drive wheels. Rocket engines produce thrust. The reaction of the fuel combusting inside the rocket creates gas, as more gas is produced pressure builds up. When the gas escapes, the thrust propels the rocket in the opposite direction. Think about what happens when you blow a balloon up. The air that you blow in the balloon is compressed by the balloon s skin; as you blow more air in, the pressure builds up. If you kept blowing air in, the pressure would be so great that eventually the skin of the balloon would break and - BANG - you know what happens then! However if you let go of the nozzle on the balloon, the air would escape through it and the balloon would be propelled in the opposite direction. Isaac Newton explained the principles that govern the motion of all objects whether they are on Earth or in space, these are called Newton s Laws of Motion: 1. Objects at rest will stay at rest and objects in motion will stay in motion until they are acted upon by an unbalanced force. 2. Force is equal to mass times acceleration. 3. For every action there is always an opposite end equal reaction. To find more information about Newton s Laws and the engineering behind rocket technology go to: http://www.nasa.gov/pdf/58269main_rockets.guide.pdf
UNDERSTANDING THE BASICS Rocket Design: Rockets have to have somewhere to carry their fuel, either inside the body of the rocket or outside in separate containers. Rockets today use either solid or liquid propellants a fuel and an oxidiser. The fuel is the chemical that burns, but the fuel wouldn t burn without oxygen so rockets have to carry enough oxygen so that burning can take place in space where there is no air. Solid fuels rockets have been used for hundreds of years, but they are not as easy to control as liquid fuel rockets; once the propellant had been ignited, it usually burns until it is all used up. Liquid propellants are a more recent invention and are more easily controlled. You can test this out by turning the nozzle on your hosepipe. When the opening is at its widest the water flows out gently, feel the force of the water. Now turn the nozzle so that the opening is smaller and the water squirts out at a higher pressure, feel the thrust of the water now.
Thread the string through the straw. Equipment: Drinking straws Balloons Thin string or Fishing line Scissors Masking tape Fix each end of the string across the room making sure it is pulled tightly. If you use fishing line make sure it is fixed high enough for people to walk under. They won t be able to see it! Inflate the balloon. Get someone to hold the nozzle shut while you attach the balloon to the straw using masking tape. Pull the straw back to one end of the string, let go of the balloon nozzle and watch it go! How far has your rocket travelled?
You could get your rocket to go further if you gave it more fuel! Try attaching two balloons to the straw. What happens if you fill one balloon up more than the other? Can you fix more than two balloons to the straw? Try a vertical launch. You ll need to get someone to fix one end of your string to the ceiling. How about getting your rocket to carry a load? Try something light at first. Attach a small plastic cup to the balloon and put a few paper clips in it. How high can you get them to go?
Rockets are more efficient and go further if the fuel is staged. Try using two balloons, one behind the other. Set up the string as before this time threading 2 straws onto the string before you fix it in place. Equipment: Drinking straws 2 Balloons Thin string or Fishing line Scissors Masking tape Polystyrene cup Cut the top off the polystyrene cup ensuring that it keeps its shape as a tube. Inflate the first balloon until it is about ¾ full. Keeping the nozzle tightly closed, feed the nozzle through the cup tube. Get someone to keep hold of the nozzle while you get the other balloon in place.
Push the front end of the second balloon through the tube and inflate. Tape both balloons to the straws so that they are parallel to the string. Place them at the end of the string. Release the rear balloon by untwisting the nozzle. The escaping air from the rear balloon should propel both balloons along. As it inflates, the second balloon should press against the tube, holding the nozzle of the first balloon closed against the edge of the tube. As it begins to deflate the pressure against the tube will lessen, releasing the nozzle of the front balloon, which then takes over.