Real Rockets

Rockets shoot skyward with massive amounts of thrust, produced by chemical reaction or air pressure. Scientists create the thrust force by shoving a lot of gas (either air itself, or the gas left over from the combustion of a propellant) out small exit holes out the back of the nozzles.

Here are two videos of real rockets being tested. The second video uses a special type of photography to see the shock waves (you will learn more about how that's done in Unit 9).

For every action, there is equal and opposite reaction. If flames shoot out of the rocket downwards, the rocket itself will soar upwards. It’s the same thing if you blow up a balloon and let it go—the air inside the balloon goes to the left, and the balloon zips off to the right. They both follow Newton's Third Law: for every action, there is an equal and opposite reaction.

What you're looking at in the video below is exactly the kind of work I did as a graduate student in college when I was 21. The end of a rocket nozzle is on the right side, and you're looking at supersonic air (made visible by a special type of photography called 'Schlieren') as a rushes past from right to left. The thick white lines are shock waves, which are lines where the pressure drop is huge. When the flow is fast enough (around Mach 2 and up), you'll see nicely shaped 'Mach Diamonds' form.

Scientists use these images to tell how well the engines will perform at high-speed flight. One of the greatest aeronautical engineers, Kelly Johnson, who founded Skunkworks at Lockheed, said the greatest compliment he ever received was when a friend commented: "It's amazing... he can actually see airflow." This is what Johnson could visualize in his mind simply because he understood the fundamentals of aerodynamics: