Final answer:
Space vehicles use Newton's third law of motion, where the action of expelling exhaust gases at high speed from the rocket engine causes an equal and opposite reaction force, known as thrust, propelling the rocket forward. Astronauts can move within a spacecraft by throwing objects, using the reaction force. Additionally, chemical reactions provide the needed thrust to launch the space vehicles.
Step-by-step explanation:
Space vehicles, like rockets, use the principles of Newton's third law of motion to blast off. This law tells us that for every action, there is an equal and opposite reaction. When a rocket engine fires, it expels exhaust gases out of the back at very high speed, exerting a large backward force on the gases. According to Newton's third law, the gases must exert an equal and opposite force on the rocket, which propels it forward. This reaction force pushing the rocket is known as thrust.
In the case of astronauts inside a spacecraft, if they were to exert a force on the inside of the vehicle, the same principle applies. The vehicle would exert an equal and opposite force back on the astronaut, affecting the measurement of the astronaut's acceleration. To move without causing recoil of the vehicle, the astronaut could throw an object in the opposite direction they wish to travel, thus using the thrown object's reaction force to propel themselves.
Chemical reactions are also involved in generating the thrust required for lift-off. In the case of the space shuttle, the main engines react liquid hydrogen with liquid oxygen, creating a huge amount of force through the rapid expulsion of water vapor. The solid rocket boosters, which are composed of ammonium perchlorate and powdered aluminum, similarly produce thrust from the chemical reaction resulting in aluminum oxide, water, nitrogen gas, and hydrogen chloride. These reactions illustrate how chemical energy is converted into kinetic energy, providing the necessary thrust to overcome gravity's pull.