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
While I only have a little knowledge on the subject, so I’ll need someone to help with some of the science verification, but hopefully I can help.
Your question seems like its two parts. To answer the part about a rocket or object ascending at a constant speed, Yes it would eventually leave earths atmosphere and eventually its significant gravitational pull, orbiting the sun in a similar orbit to earth due to the orbital momentum it still had. Depending on the direction it was going after leaving earth, there’s a lot that could happen.
For that object to maintain that speed, it would have to have a force pushing it upwards continuously, such as the engines on a rocket or the propeller on a helicopter. This is due to the a combination of things such as air resistance, (which doesn’t quite “push it down” so much as resisting its movement. Kind of like pushing your hand through mud, only with a lot less resistance.) and the gravitational pull of earth on it, (which does pull it down).
For the answer about practical rockets such as space craft, it gets a bit more complicated. For those, the goal is usually to get into an orbit. It’s usually easier to gain the speed necessary when there’s still atmosphere for the engines to push against. You want enough speed to escape the atmosphere, but not so much that the air resistance on the front of the craft generates excessive heat or begins to resist the craft in greater proportion than the thrust you’re generating to maintain that speed. The higher you go, the less air resistance, meaning you can go faster before achieving orbit. What’s interesting that we’ve discovered, is that its actually more efficient to go a little sideways so that you don’t have to fight gravity/air resistance as much, saving fuel, weight, and money. This is where it gets a little hard for me to explain through text. Once you begin tilting in a horizontal direction, not only do you begin building the horizontal velocity needed for orbit, but because the rocket is heading so fast, some of the air is pushed under the rocket, generating a (relatively) small amount of lift. Similar to how aircraft wings generate the lift needed to keep the craft flying, just on a much less wing-like surface. However, This needs an incredible amount of both speed and constant acceleration to maintain and continue getting higher. The speed is also needed due to the massive weight of the rocket, and relatively small surface area on the bottom for the lift.
Once you leave the atmosphere, this is where my knowledge gets very spotty. You no longer have to worry about air resistance slowing the craft or anything, just finishing achieving the orbit you want.
If you want so great videos on stuff like this, check out Scott Manley on YouTube and his KSP videos! Hope this helped!
Edit: I can’t seem to find any obvious videos by him on the subject, but there’s probably some out there that showcase this better than I can explain it.
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