If you push horizontally on your book with a force of 3 N to make the book slide at constant velocity, how much is the force of friction on the book? The action of the rocket is similar to releasing a balloon that zips across a room. In the case of the Shuttle, the main engines ran at 65% for the first minute or so of the flight. So tl;dr, can't answer the question until you give more variables :). A rocket in its simplest form is a chamber enclosinga gas under pressure. I'm just speculating; I don't know. Like a feather, the light person reaches terminal speed sooner, while the heavy person continues to accelerate until a greater terminal speed is reached. The action is the … 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). But I don't think it's fair to say "a moment's thinking shows it's wrong". From the earth’s surface, a rocket is fired horizontally. By using our Services or clicking I agree, you agree to our use of cookies. Now we deal with the case where the mass of an object is changing. If you move your hand upwards vertically at a constant speed and then someone pulls it down, it will slow down or go bac in the oposite direction. Gravity, being a vertical force, causes a vertical acceleration. At that time it is fully loaded with fuel and hence its acceleration is slow. Why don't rockets tip over when they launch? If you take too long, the rocket will have hit the ground (as per your answer) and as that will happen relatively rapidly, terminal velocity is not really going to become a major factor here. 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. All else being equal, the rocket accelerates faster downward, because gravity helps. The answer is "the TV people got it wrong", and that's that. Television is stupid, and QI got it wrong. Imagine a setup whereby the laser is placed horizontally inside a rocket and points toward a detector which tells the rocket to accelerate. But you will also hit terminal velocity in the other directions as well. Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Which is why I worded my answer the way I did. Can a computer determine whether a mathematical statement is true or not? thanks for all the replies guys but what if i were to ask which one would accelerate faster. What's easier, walking on flat land or trying to walk up a very steep slope? Furthermore, in a Hohmann transfer you are making two burns. The rocket's engine produces a horizontal acceleration of 2. This force will cause him to start to accelerate in the vertical direction. The vertical rocket could travel faster, the horizontal rocket could travel faster, or they could both travel the same (mean) speed...depending on the propulsion force and duration of that force. 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. 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. The three most significant forces would be: Going vertically, the rocket's (simplified) vertical speed would be: Going horizontally, the rocket's (simplified) horizontal speed would be: Up until the horizontal rocket hit the ground of course, which could occur while there was still propulsion, in which case friction with the ground would significantly slow the mean speed. Need more information. At that kind of acceleration gravity is negligible. If it is the mean speed during propulsion, it depends. 0 m / s in the horizontal direction of from the roof of a 3 7. Without more constraints, the answer to this question gets complicated. As he falls he will be going faster and faster in the vertical direction . Non-plastic cutting board that can be cleaned in a dishwasher. 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. Why not land SpaceX's Starship like a plane? As a rocket is fired from a launching pad, its speed and acceleration increase with time as its engines continue to operate. This reminds me of why beds are extremely dangerous: that is where most people die. 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. Why do rockets accelerate fastest horizontally? A toy rocket is launched with an initial velocity of 1 2. Cookies help us deliver our Services. The slope of the velocity graph during this time gives a vertical acceleration of 1.8 m/s 2. Same answers to "which would travel faster" apply here. It has a constant acceleration of 17.5m/s^2 for the first 1.5 s. Then its fuel is exhausted, and it is in free fall. Use MathJax to format equations. What is the deceleration of the rocket sled if it comes to rest in 1.1 s from a speed of 1000 km/h? Assuming it wasn't destroyed by the drag forces, it would either orbit the earth and never become as fast as the vertical rocket will eventually become (max speed), or it would leave the earth and effectively have the same forces acting on it as the vertical rocket (and the mean speeds could approach each other). Cont. Only then was it throttled up to 100%, increasing acceleration. I've heard that rockets accelerate fastest when travelling horizontally to the ground, not downwards or upwards. The concept affects backslider rockets greatly. (Such deceleration caused one test subject to black out and have temporary blindness.) It's just a TV quiz show, maybe they made a mistake. Explain Like I'm Five is the best forum and archive on the internet for layperson-friendly explanations. First, the greater the exhaust velocity of the gases relative to the rocket, v e, the greater the acceleration is.The practical limit for v e is about 2.5 × 10 3 m/s for conventional (non-nuclear) hot-gas propulsion systems. To move from one orbit to an orbit that is further out you want to add energy to your rocket. The exceptions would be ballistic missiles, which launch vertically only to set up their trajectory arc, their later horizontal acceleration being due to gravity alone. When fired, it uses this energy to accelerate. Given enough fuel and a long enough timeline, the vertical rocket's mean speed could be greater. - When increasing your orbital radius this is one burn to raise your apoapsis, and one burn to raise your periapsis. Ultimately, all energy becomes heat. 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). 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. ... A rocket becomes progressively easier to accelerate as it travels through outer space. It will just take longer as acceleration is lower. With no external forces on the rocket-gas system, the rocket’s momentum must increase in the forward direction. http://www.aerospaceweb.org/question/aerodynamics/q0025.shtml, Opt-in alpha test for a new Stacks editor, Visual design changes to the review queues. It only takes a minute to sign up. See http://www.aerospaceweb.org/question/aerodynamics/q0025.shtml. The flame is not pushing against the air, and the air has nothing at all to do with it. Meaning of "and light shows between his tightly buttoned torso and his father’s leg.". Air inside a balloon is compressed by the balloon's rubber walls. The more goes to potential energy – that is, the higher the rocket rises – the less can go to motion energy (aka speed). With space rocket… They made a mistake. 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. Because the acceleration is inversely proportional to the mass the rocket will be accelerating significantly faster at that point. Is that true, and why? Don't listen to people. Someone said "downwards" but the correct answer was horizontal. I think this question is too trivial--- it is only nontrivial because somebody said something stupid (namely that horizontal is faster than downward), and a moment's thinking shows this is wrong. It will speed up. On both periapsis and apoapsis your trajectory is parallel to the ground, and so you get the highest efficiency when accelerating horizontally. The horizontal rocket needs to adjust to fight gravity, just as the vertical one does. However, in order to achieve orbit, the rocket has to travel 7 km/sec horizontally. Can I draw a better image? Projectiles are objects upon which the only force is gravity. Press J to jump to the feed. It would travel faster because it would not have to be fighting gravity. You are still fighting gravity if the rocket is going horizontally. They are in essence, rocket powered aeroplanes, with 'lift' carrying the bulk of the weight as it flies horizontally, allowing for greater acceleration. The faster it goes, the more heat is created that way. This is how Earth-centered cosmology survived for thousands of years--- thousands of students saying "I think the Earth rotates" and the expert saying "Although it looks like it, it's not so!" maybe gravity doesn't apply if you're already going faster than terminal velocity by your own propulsion, so it doesn't increase your rate of acceleration, and maybe the air pressure behind the rocket when falling doesn't provide as much push. It was a question on the BBC panel show 'QI' hosted by Stephen Fry. Now, in reality there's a third kind of energy that's being created, and that's heat. 0 m tall building. A model rocket is fired vertically from rest. Question. If you try to plot the formula as function of Ve with fixed V, you'll see that higher Ve yields higher efficiency. Over time the rocket loses mass as it burns up fuel. However from an outside observer inertial frame of reference he will notice the light is being bends, so does the rocket still accelerate? 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. Don't Panic! But still, horizontal = faster. 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). 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). It's not an answerable question given the lack of facts such as: How far above sea level is the horizontal rocket.How far vertically is the other rocket travelling. The rocket accelerates in the positive direction and increases its velocity. According to Newton’s third law, the expanding hot gases exert a reaction force that pushes up on the rocket. Thus the gas, originally at rest in the rocket, is given a large momentum backward. 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). Rory Alsop explained why the idea is wrong, but it may originated from the following reasoning. Looking at this problem as what is happening horizontally and vertically , you should get the idea that this is just like the components that we were just working on a couple of lessons back. Hence, the rocket accelerates faster when it is going horizontally. What limits the velocity of ships such as voyager 1? The majority of surface to air, air to air etc. When a rocket’s motor is fired it expels gas at a high velocity backward. If it's the max speed, it depends. Sure. Explaining why dragons leave eggs for their slayers, Why didn't Escobar's hippos introduced in a single event die out due to inbreeding. But in the meantime, it's accelerating faster in the other direction. That means that the rocket's mass gets smaller during flight. Unless it is on the ground, it is fighting gravity. And somehow I still managed to get a downvote. Can anyone identify the Make and Model of this nosed-over plane? does that mean that the rocket's acceleration is increasing at a greater rate when it is losing mass due to fuel consumption that if it were not? In a nutshell, a rocket must curve its trajectory post-launch, if it wants to enter the Earth’s orbit. missiles use a combination of fins and a specialised shape to give a stable lifting surface. The result is effectively two or more rockets stacked on top of or attached next to each other. The fuel that the rocket consequently saves can be used to accelerate it horizontally, in order to attain a high speed, and more easily enter the orbit. Escape velocity is calculated on the assumption that the only force applying is gravity, that is, only after the rocket engines (or whatever accelerated you to 11km/s) have stopped firing. So you can see that it will accelerate fastest downwards. In both cases, there are several forces at play. 12. Only until it hits terminal velocity. So the answer really depends on what the OP means by "travel faster." But you are not correct in saying that the air gives reaction. The force of gravity would affect the horizontal rocket significantly less (possibly a negligible unmeasurable amount), but it will have an effect. 36. Vietnamese Coffee (cocktail) - what to sub for condensed milk? When the vertical rocket goes higher the drag diminishes as the level of air resistance reduces. Hence, the rocket accelerates faster when it is going horizontally. So, since all energy has to go somewhere it either goes to potential energy or motional energy (sorry if those words are not 100% correct, I'm not a native speaker you see). Even if the rockets were propelled at a lower speed for only a very short distance, the earth would curve away to some degree. MathJax reference. But, the ball still has kinetic energy in the horizontal direction. On this page we show the events in the flight of a water rocket. When a backslider is made correctly, it turns horizontally and spins sort of like a fan would. As it happens in reality, the rocket launches mostly in a vertical state, and the atmospheric density decreases quite rapidly with altitude. Why do large rockets make “popping” sounds during liftoff? (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. What's an umbrella term for academic articles, theses, reports, etc.? A moment's thinking shows that it is wrong, and the person who said "downward" did this moment's thinking. From the earth’s surface, a rocket is fired horizontally. They are in essence, rocket powered aeroplanes, with 'lift' carrying the bulk of the weight as it flies horizontally, allowing for greater acceleration. When a net force acts on an object, its acceleration depends on the object's The correct answer is downwards. But that doesn't play a big role for the question you asked, just as the motion energy for the air pushed aside (given movement) doesn't influence the outcome in any significant way. 2 m / s 2, in the same direction as the initial velocity, but in the vertical direction the acceleration is 9. Hint: You must use two conservation laws. A small opening at oneend of the chamber allows the gas to escape, and indoing so provides a thrust that propels the rocket inthe opposite direction. @RonMaimon Your attitude is a bit harsh. Press question mark to learn the rest of the keyboard shortcuts. Also, certain anti ballistic missiles like the Sprint, which has bonkers acceleration, reaching Mach 10 in 5 seconds. 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! (assume constant acceleration and no … Energy (or mass) never disappear and never comes from nothing. Do rockets require stabilization so they don't wobble or even spin? But surely you need to take the most obvious case - which is from zero to x seconds. 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). And then its acceleration becomes 0. In order for the left side of our equation to remain in balance with the right side, acceleration of the rocket has to increase as its mass decreases. Going vertically, eventually gravity and air resistance become smaller and smaller factors, until the rocket enters outer space and drag and gravity become negligible forces. Supervisor has said some very disgusting things online, should I pull my name from our paper? At the same time, because the rocket is now fairly high up, the air pressure has dropped significantly, and the reduced drag also increases acceleration. Think about it this way, if you move your hand horizontally at a constant speed and then someone else pulls it down vertically, the horizontal speed will not change will it? $\begingroup$ Rocket should accelerate a payload to given fixed velocity V. (For example V=7.8 km/s for launch to low Earth orbit). That is why a rocket starts off moving slowly and goes faster and faster as it … So you heard wrong. E.g. 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. I get annoyed when somebody says something right, and then expert say "no, counterintuitively, the obvious thing you said is not right!" To achieve that, after a while the rocket's path starts to curve towards the horizontal. Because of this, the engines may not be run at full power until past the "max-q" point. New comments cannot be posted and votes cannot be cast, More posts from the explainlikeimfive community. What is a common failure rate in postal voting? The rocket has a certain amount of energy at its disposal. I chopped through 1/3 of the width of the cord leading to my angle grinder - it still works should I replace the cord? Once the rocket runs out of fuel, it'll use that energy to fall back to earth (unless you escape the earths gravitational field, but that's a whole different cat). When you watch a video of a space rocket take-off, it seems to crawl along the launch tower. Yes, remember Newton's law [itex]F = ma[/itex], so the same force will acclerate an object of a lower mass faster. Explain why this occurs even though the thrust of the engines remains constant. 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. How far does it travel and for how long does it travel before it hits the ground? To learn more, see our tips on writing great answers. more, the rocket must be aerodynamically stable during flight. There's no confounding factor. The vertical velocity changes by -9.8 m/s each second of motion. 8 m / s 2, downward. Water rockets are among the simplest type of rocket that a student encounters. 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. I was just speculating to demonstrate that it's not, @callum: TV makes mistakes, it's not internet. The horizontal rocket isn't fighting against gravity, and thus would accelerate more quickly. When it. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. This is obvious, no matter what anybody says. The stuff you say after your first sentences is nonsense, and it is a stupid question. The air pushes back so thatthe forces on each side are balanced.When the nozzleis released, air escapes through itand the balloon is propelled in the opposite direction. Thanks for contributing an answer to Physics Stack Exchange! When a rocket engine fires, you can see the action - all the flame and hot gasses being ejected out the back. At the same time, because the rocket is now fairly high up, the air pressure has dropped significantly, and the reduced drag also increases acceleration. What must be this initial velocity if the rocket is to orbit at a radius of 3.81E07 m from the center of the earth? 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. If the rocket moves fast enough horizontally, the earth will curve away from it faster than it falls. A backslider rocket is a rocket that when it begins free fall, turns horizontally and starts to spin and rotate on its center of gravity to increase fluid friction. In this case, the rocket wizzing through the atmosphere heats up the air it rushes through (and its hull). A good example of this is aballoon. How big does a planet have to be to appear flat for human sized observer? A bullet is fired horizontally from a rifle 1.5m from the ground at 430m/s. This is most efficiently done by adding thrust in the direction you are traveling. How long are these hypothetical rockets propelled for? But my point is, don't dismiss it as a stupid question. If you were to tie a string around the rocket at its CM, it would balance from the string horizontally. Accelerating upwards, the rocket can accelerate at T-g, where T is thrust, and g is the acceleration due to Earth's gravity. The fired bullet was moving horizontally so that the air resistance was only in the x-direction. A multistage rocket, or step rocket, [citation needed] is a launch vehicle that uses two or more rocket stages, each of which contains its own engines and propellant.A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. When a space rocket takes of, it does so vertically. If the horizontal rocket travelled fast enough, the earth could curve away from the rocket faster than it fell. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. (Hint: About 90% of the mass of a newly launched rocket is fuel.) Also, lift isn't needed since the thrust is sufficient to carry the weight of the rocket. An object will accelerate when it is pushed or pulled with a net force. Likewise, most of the rest of the energy produced from the fuel is turned into motion energy (speed, movement). A rocket’s acceleration depends on three major factors, consistent with the equation for acceleration of a rocket. If it didn’t do that and continued to go straight up, it would eventually reach a point where its fuel would run out and, most likely, it would end up … The body of the rocket … Why is this so? Assuming that air resistance is negligable. The variable is Ve. Why is this plot drawn so poorly? Making statements based on opinion; back them up with references or personal experience. Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The relative magnitude and direction of the forces determines the flight trajectory of the rocket. (a) Ignoring air resistance, how high does the rocket travel? Tool to help precision drill 4 holes in a wall? Because the acceleration is inversely proportional to the mass the rocket will be accelerating significantly faster at that point.

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