The main objective of the rocket engine is not only to get the cargo above the atmosphere, but more importantly to accelerate it in horizontal direction to the orbital speed (7.5 km/s for the orbital altitudes of the Shuttle and International Space Station). In both cases, there are several forces at play. I get annoyed when somebody says something right, and then expert say "no, counterintuitively, the obvious thing you said is not right!" But you are not correct in saying that the air gives reaction. (a)The pressure generated by the burning rocket fuel provides an action force that causes the expanding hot gases to accelerate from the bottom of the rocket. Now we deal with the case where the mass of an object is changing. Most every other rocket type functions in the same way, because of the advantages lift confers, even if only the body of the rocket is providing it. Assuming that air resistance is negligable. Less Air Resistance, and there is gravity which prevents not only prevents the rocket from moving quickly but also slows it at down (at about 9.8 meters per second squared). Explain Like I'm Five is the best forum and archive on the internet for layperson-friendly explanations. On both periapsis and apoapsis your trajectory is parallel to the ground, and so you get the highest efficiency when accelerating horizontally. Now, when you're in a gravitational field (as you are when you are on earth), if you go away from the gravitational center, you add potential (or elevation or position) energy. Rockets can accelerate even when the exhaust relative velocity is moving slower than the rocket (meaning ve is in the same direction as the rocket velocity). To learn more, see our tips on writing great answers. If you try to plot the formula as function of Ve with fixed V, you'll see that higher Ve yields higher efficiency. You are still fighting gravity if the rocket is going horizontally. I've heard that rockets accelerate fastest when travelling horizontally to the ground, not downwards or upwards. Over time the rocket loses mass as it burns up fuel. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. Cont. If you were in a rocket accelerating at 32ft/sec^2 in space, you would use fuel at the same rate as a rocket 100 feet in the air above the earth sitting stationary on a plume of exhaust (because it too is notionally accelerating at 32ft/sec^2, exactly counterbalancing gravity). It's just a TV quiz show, maybe they made a mistake. The horizontal rocket needs to adjust to fight gravity, just as the vertical one does. This differs from propeller engines or air breathing jet engines, which have a limiting speed equal to the speed at which the engine can move the air (while in a stationary position). What is the deceleration of the rocket sled if it comes to rest in 1.1 s from a speed of 1000 km/h? Now, if the rocket flew horizontally, or if the atmosphere extended upwards forever, the drag force would increase and increase and increase as the rocket got faster and faster and faster. At that kind of acceleration gravity is negligible. Thanks for contributing an answer to Physics Stack Exchange! Accelerating downwards, the rocket can accelerate at T+g, Accelerating horizontally, the acceleration will be T. Asking for help, clarification, or responding to other answers. Question. But, the ball still has kinetic energy in the horizontal direction. So the answer really depends on what the OP means by "travel faster." When you watch a video of a space rocket take-off, it seems to crawl along the launch tower. Likewise, most of the rest of the energy produced from the fuel is turned into motion energy (speed, movement). Which is why I worded my answer the way I did. At that point the first stage may already have dropped off and a large amount of fuel has been burned, so the rocket is a lot lighter. Without more constraints, the answer to this question gets complicated. The variable is Ve. See http://www.aerospaceweb.org/question/aerodynamics/q0025.shtml. But you will also hit terminal velocity in the other directions as well. A rocket fired into space contains its own oxygen and fuel (perhaps liquid hydrogen and liquid oxygen) and needs no air for combustion (a ram jet must take in or ram air for fuel combustion). Most every other rocket type functions in the same way, because of the advantages lift confers, even if only the body of the rocket is providing it. ... A rocket becomes progressively easier to accelerate as it travels through outer space. Air inside a balloon is compressed by the balloon's rubber walls. As he falls he will be going faster and faster in the vertical direction . @RonMaimon Your attitude is a bit harsh. Somebody could then take that as meaning "faster than upwards as well as downwards", Another issue is the is the "dynamic pressure" which is created by the speed and air-drag. Explain why this occurs even though the thrust of the engines remains constant. If it is the mean speed during propulsion, it depends. On the other hand, the horizontal acceleration is 0 m/s/s and the projectile continues with a constant horizontal velocity throughout its entire trajectory. Yes, remember Newton's law [itex]F = ma[/itex], so the same force will acclerate an object of a lower mass faster. The slope of the velocity graph during this time gives a vertical acceleration of 1.8 m/s 2. At that time it is fully loaded with fuel and hence its acceleration is slow. The action is the … The most efficient way to raise your apoapsis is to burn at periapsis, and the most efficient way to raise your periapsis is to burn at apoapsis. In this case, the rocket wizzing through the atmosphere heats up the air it rushes through (and its hull). $\begingroup$ Rocket should accelerate a payload to given fixed velocity V. (For example V=7.8 km/s for launch to low Earth orbit). Because of this, the engines may not be run at full power until past the "max-q" point. The thrust needed to launch the space shuttle is provided by two solid rockets and three space shuttle engines, all of which operate during lift-off.According to NASA, the thrust provided by the two solid boosters is 6.6 million pounds, whereas the three engines of the shuttle provide almost 1.2 million pounds’ worth thrust.This means the total thrust during a launch is 7.8 million pounds! Only then was it throttled up to 100%, increasing acceleration. Is that true, and why? To increase the stability of the rocket there are two principles you need to understand: Center of Mass (CM) - The point at which the rocket balances. And then its acceleration becomes 0. The rocket's engine produces a horizontal acceleration of 2. Thus the gas, originally at rest in the rocket, is given a large momentum backward. There's no confounding factor. rev 2021.2.12.38571, The best answers are voted up and rise to the top, Physics Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. thanks for all the replies guys but what if i were to ask which one would accelerate faster. Press J to jump to the feed. When a rocket engine fires, you can see the action - all the flame and hot gasses being ejected out the back. (Such deceleration caused one test subject to black out and have temporary blindness.) It will speed up. This is obvious, no matter what anybody says. Why is this so? The direction of gravity will change so that it is no longer truly horizontal relative to the direction of the gravitational force and gravity will significantly affect its speed in the direction it is being propelled.