Edit: I didn’t understand how a jet engine worked, but now that I do, the question has been amended to this…
“Why does a rocket have to travel faster and faster the higher up it goes? Shouldn’t it require less and less speed as it is further from the earth it gets because there is a non-zero number(very small) of negative gravity change the higher you are?”
Edit #2: I think I suck at asking this so I’ll ask it like a 5 year old.
We have all seen videos of rockets taking off. They start very slowly, and then build in speed. Although, at first, they build up in speed. It’s not as if they torque off the earth at 20,000mph, although that would be ASTOUNDING to see. So here’s my super drawn out really dumb question that I cannot wrap my head around the answer for the life of me.
Let’s say you have a rocket going 100mph going 90 degrees straight up from the surface of the earth. Why can’t it just keep going 100mph straight up. Just keep going and going. Up, straight up. Up up up and away? Why can it move up starting from zero miles an hour? If it can move up at 5mph even for an instant, why can’t it continue at that velocity all the way up.
All the answers have been wonderful if I was asking how to get something in orbit. I’m asking why 100mph 90 degrees going straight up works down here, but not up there? I cannot find a straight answer to this question no matter what I google. I appear to be bad at research or this is just a stupid ass question. I really just don’t understand the physics of this at all.
Let’s try this another way. Say I threw a magic baseball that whatever velocity it was tossed at, it maintained until it hit a object. It doesn’t disregard gravity. It just has a magic anaerobic motor that maintains the speed. Like cruise control. Say I throw it 90 degrees straight up at 35mph. Will it leave Earth? Why or why not?
In: Engineering
That’s like asking why can’t a submarine drive above water.
There is a lack of air density and oxygen at high altitudes. You need air density for lift to be created by wings, and you need oxygen for the engines to create combustion.
Because a jet engine takes in air at the front and shoves it out the back to make thrust. There isn’t air in space to suck in.
I mean, with the right conditions you might be able to get it into space. But without a rocket or some other propulsion you’re either going to fly off into the void or more likely get pulled back by gravity
As an aside… it is quite easy to build a rocket to get to space. You can basically launch one from your back yard.
The problem is that to STAY in space, you need to get going 25,000mph laterally. That is the tricky part.
Next to you watch a rocket launch notice that they don’t go straight up. Almost immediately they start flying sideways in order to build lateral velocity.
The way jet engines work is by pushing air backward. As you get higher, the air gets thinner and jet engines become less effective. Once you get high enough, a jet engine won’t work at all.
That being said, if a fighter jet used a rocket instead, there would still be issues. Space ships are CRAZY fast. Just to be able to stay in space where the international space station is, you have to go over mach 20. That takes way more fuel than a jet can hold.. at least for now :P. If you want to go slower and stay in space you have to go higher, and again, have more fuel.
Final note, since there’s no air in space an airplane’s wings won’t work either. The plane won’t be able to turn or pitch, and anything that helped it stay in the air before won’t do it much good now
You’re correct in that at higher orbits in space an object can travel at a lower speed. However, to increase orbital altitude requires an increase in speed, which let’s you go further from Earth as you slow down. As you reach the furthest point, the object will start to speed up as it’s orbit again gets closer to the Earth, ending up with an elliptical orbit.
There’s a saying in orbital mechanics: “you have to speed up to slow down.”
I don’t think rockets *have* to travel faster and faster the higher it goes – I think they just *do*, since it’s a byproduct of rocket engine design. Rockets burn fuel at a constant rate (at least solid fuel rockets do); however, the weight of the rocket goes down as fuel is burned, and air resistance goes down as the rocket climbs and the atmosphere thins. Therefore, the rocket keeps burning fuel and keeps accelerating, and accelerates at an even faster rate as weight and air resistance decrease.
Whether you’re trying to enter an orbit around the Earth or trying to reach escape velocity and leave Earth entirely, you need to reach a certain speed. Rockets get faster the further up they go because there’s less and less air resistance up there. Moving quickly through the thick atmosphere would quickly break the rocket apart. If a rocket could just instantaneously achieve its desired velocity without breaking apart, that’s probably would they would do.
You don’t need to move faster the higher up you go. But in order to stay up you need enough speed to stay in orbit or you will fall to the earth. To understand this, you have to understand orbit. An object in orbit is actually not “driving itself”, it’s constantly falling. It’s similar to swinging an object around with a string. The objects velocity keeps it moving and the string keeps it from moving away from the object it’s tied to. For orbit around the earth, gravity acts as the string. For it to work, your speed and height need to be calibrated correctly. Too fast and you’ll keep going out into space, and too slow and you’ll dive back to earth. The further away from the earth you are, the less the force of gravity acts on you and the slower you need to go to stay in orbit.
To answer your edit, The ISS experiences 99% of the gravity we do, IIRC. Even the moon experiences a lot of Earth’s pull.
Edit: Apparently I misremembered. [this](https://www.wired.com/story/yes-there-is-gravity-in-space/) article says 88%. point still stands
To stay in space, you have to enter an orbit. the ELI5 answer to this is, you have to go so fast, that by the time earth pulls you down, you go far enough to the side to miss it.
Of course it’s much more complicated than that. Orbital mechanics can be very daunting, but if you are willing to put in some effort, KSP can make you a rocket scientist before you even notice.
>”Why does a rocket have to travel faster and faster the higher up it goes? Shouldn’t it require less and less speed as it is further from the earth it gets because there is a non-zero number(very small) of negative gravity change the higher you are?”
You are right that the speed needed to overcome gravity (escape velocity) reduces as you climb…but not substantially until you’ve gone several hundred miles already. (Gravitational force is half at sqrt(2) earth Radii, or about 1600 miles above the surface.) And if you’ve made it that far you’re going pretty fast already.
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