Index Top of Module Bottom of ModuleVelocity and VelocityRocket Physics – Equations of MotionA space shuttle or rocket is certainly one of the most complex structures that can ever be built. It takes the best engineers to build one successfully, because if something goes wrong, lives and billions of dollars will be lost. This is where physics comes into play. In fact, it plays an important role in ensuring that everything is in place. Many laws of physics are used, but we will specifically look at one important one, Newton's Law of Motion. There are three laws given to us by Sir Isaac Newton: The first law states that a body will remain at rest or in motion in a straight line unless affected by a force. The second law states that the variation of movement is proportional to the applied force and parallel to it. The third law states that for every action there is an equal and opposite reaction. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay According to Newton's first law, two things are really economical: inertia and standing still. In space, sitting is a little hard to define, I mean compared to the Sun or Mars? Also, most of the time we are in some sort of orbit, so standing still doesn't really make sense. What we need to think about is how to go from one type of orbit to another type of orbit. Newton's Third Law holds the "secret" of rocket propulsion for space travel. See the following figure. If A exerts a force on B, then B exerts an equal and opposite force on A. Or, in the case of space travel, if a mass (m) of fuel is expelled from a rocket's exhaust, the rocket will accelerate in the opposite direction to the one where the waste fuel went. What happens to the spacecraft immediately after the rockets are turned off? Top of the shape Slow down like a plane does here on Earth until it comes to a complete stop. However, unlike a plane that must contend with Earth's gravity, the spacecraft will continue to go in the same direction as it slows down. Astronauts will simply have to fire the rocket engines again to keep moving. The spacecraft will continue to coast at the same speed and in the same direction. The spacecraft will slow to a complete stop. Additionally, the ship will veer off course in the process of slowing down because the astronauts cannot use the flaps on the spacecraft's wings to steer. Bottom of the shapeAs the engines fire, the spacecraft accelerates. When it has reached the intended speed, the rockets are turned off. This means that it is now in some sort of orbit around the Earth or around the Sun. It will remain in this orbit until its rockets are launched again. Its velocity will be constant, except for the very slow changes that are part of its orbital motion. Having answered the previous question, you should now understand that coasting, as a result of Newton's first law, is a vitally important aspect of space travel. The reason this is so is because it means astronauts only have to turn on their engines for a short time and then head towards a planet. But what happens when they arrive on a planet? If they don't slow down they could crash their ship into the planet. The simple answer to the last question is that a spacecraft must use fuel to both slow down and accelerate. When a spacecraft moves forward, again using Newton's laws, astronauts must launch their rockets in that direction to create an opposing force. In a later unit we will look at this more..