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There are four main science principles that have to do with flight: thrust, weight, lift,and drag. Thrustis the motion that makes an airplane move forward, and a rocket move up. What works against thrust is weight, or the natural force of gravity on an object. The weightof a plane or rocket is always pulling it down, so in order for it to fly, it has to have more thrust than weight. Liftis the force that lifts things up! For birds and airplanes, lift is caused by air moving around their wings, creating pressure that keeps them up. Lift keeps airplanes in the sky, while thrust givesthem power to move forward. The last thing you need to know about flight is something called drag, or the natural force that resists the motion of an object. Dragis the opposite of thrust, so for flight to take place, the thrust at play must be equal to or greater than the drag. If the amount of drag becomes larger than the amount of thrust, the plane will slow down. If the thrust is increased so that it’s greater than the drag, the plane will speed up.
Blasting Off into Space
Unlike airplane engines, a rocket carries its own supply of oxygen to burn its fuel. That is why it can work in space, where there is no air. Before a spaceship (also called a space shuttle) can get up in space, it needs to be launched by a rocket.
A rocket can be defined simply as “a chamber enclosing gas under pressure.” A small opening allows the gas to escape, causing thrust. When a rocket blasts off, fuel (such as gasoline) and an oxidizer, which is a substance (such as liquid oxygen) that chemically combines another substance with oxygen, are heated and mixed to create a burst of gases. These gases move so fast and are so powerful that as they escape through the nozzle and hit the ground, they push the heavy rocket up into the sky. As more fuel is added, the rocket keeps going further and further into space.
Since the thrust of a rocket depends on how the gas escapes, one of the most important parts of a rocket is the nozzle. The nozzleis the opening that lets the gasses out. When the opening is made smaller, the acceleration of the escaping gas increases. Use the spray nozzle on your garden hose to see how it works. When you twist the nozzle so that the opening is bigger, the water doesn’t spray as far. The smaller the opening is, the farther and harder the water sprays out. It works the same way on a rocket: the smaller the opening, the more thrust caused by the escaping gas.