That’s why I didn’t mention it before and btw it was a basic study..
That’s I am not dealing with these terms I am dealing with movements in in linear directions. forward and back etc. when I say acceleration I mean speeding up.
vyVY
The subject is about a constant force applied to an object not an object sailing through space on its own. vyVY
In this case, the speed is fixed by the fact that you personally are going at 5mph. Presumably in this case you are able to apply just enough force to overcome the rolling resistance to push the car. If the car was easier to push, you could push it faster. If someone in the car hit the brakes, you’d be pushing it more slowly if at all.
OK, so now you’re in a case where the car is floating with no gravity or air. You are walking next to it (somehow you still have gravity to walk, despite the car not having gravity applied to it, I guess you have magnetic boots) at 5mph. What you will find in this case is that it takes you no effort whatsoever to keep the car moving. Once you get the car up to 5mph, it will keep going at that speed with no more force required to keep it going. You’re not pushing it at this point, just walking next to it as it drifts freely along. You could have two cars or a dozen going at the same speed, the only difference it will make is that it takes longer for you to push them up to speed. Again, the 5mph limit is purely based on how fast you can walk in your magnetic-boot spacesuit.
Assume that you have a genie who is providing you with an endless supply of air. You sit on the back of the car and blow backwards at 5mph. This doesn’t accelerate you very quickly, you can’t blow air that hard, but you will accelerate. The car is moving, but so are you, since you’re sitting on the back of the car. Eventually you and the car reach a speed 5mph faster than you were going when you started. You’re still blowing air, and that’s still causing you to accelerate. This will keep up forever - as long as your magic genie provides you with air, you’ll keep accelerating forever. (well, light speed limit and relativity will eventually cause strange stuff to happen, but we’ll ignore that for this thought experiment.)
The car doesn’t remember how fast it was going when we started moving. I’m not walking on anything next to it, so there’s no 5mph speed limit from your legs pushing against the ground. As long as you keep applying thrust by blowing air backwards, the car will keep accelerating.
Let me propose a thought experiment for you to consider. Let’s say I get a little balsa wood cart and attach a balloon to the back. If I inflate the balloon, then release the car, the air jetting out the back of the car will push it up to 5mph before running out.
Now I take this car and get on an airplane. The pilot takes off and we’re flying at 600mph through the air. I take my little balloon cart, blow up the balloon, put it down inside the plane, and let it go. It jets forward, going 5mph relative to me, and 605mph relative to someone on the ground. How is it going at 605mph when the force from the air blowing out the back is only enough to make it go 5mph?
Correct me if I am wrong, in a vacuum we fall to earth at the same time no matter what the weight? so a 700lb man would hit the ground at the same time as a 7 lb baby? though the same force is acting on them? If you add another 700 lb man to the first one they will still arrive on earth at the same time. the men wouldn’t slow down or speed up. What is the significance of these forces adding up. the speed of falling is the same.for the 700 man to speed up over the speed of the baby you need something pushing him faster than he is going now. The thing pushing him faster is what i call the force more force so to speak, if that is not the correct name tell me what it is.
vyVY
Each of those weights feel different forces. But because they are different masses as well, they end up with the same acceleration. The “thing pushing him faster” is the acceleration. The ‘a’ in ‘F=ma’.
would you rather I said I had a stick form earth into space, then you get into earth rotation etc.? please use the illustration for what it is.
Once again; would you rather I said i had an endless supply of air in a bottle or the illustration?
I said if a wind meter was clocking the air at 5mph.
remember The air is blowing out at 5mph
Or the magic bottle!
This means speeding up I assume
Could we ignore the magic genie also?
but my wind gauge does, a constant 5mph stream in one direction.
Ok maybe in this case you are right, this one i don’t have the capacity to understand this one right now.
Is there anyway to measure the thrust in the direction of the car? Is is possible to say as an example that 5 lbs of thrust are producing the five mph wind that is registering on the wind meter? And if so are you saying that this five pounds of thrust can eventually get the car moving at near the speed of light?
Because the force of the plane is blowing the plane at 600 mph and you are inside the plane as the earth is rotating at 1040 mph so we all are moving 1040 mph plus our speed on the ground and add the speed we go around the sun and so on.Sorry I fail to see how this is relevant
vyVY
Bump… anyone get a chance to deal with this yet? :
Imagine a ten mile long tube north to south orientation; with one end open, in the vacuum of space. so no air is in the tube. have a fuel air mixture and light it. I guarantee you that before that expansion of gasses reaches that opening ten miles away that canister is on the move. why? because the expansion of gases expanding to the north hits the closed end of the tube.
What folks are saying in here is that we have to wait until the expansion goes ten miles and exits the tube before you have movement, which is absurd!!
That tube is long on its way from the north force. Its the south force vector you feel coming out the tube…
vyVY
btw the bump post puts in a nutshell in excellent laymans terms of what i have been trying to get you to understand what goes on in the engine. If you can see this then you will begin to hopefully see my other points in a different light
vyVY
Good, but what they seem to be saying is that if you have two things the same mass and two DIFFERENT forces moving them in the same direction they will eventually end up at equal speeds albeit up to the speed of light. This is what I can’t grasp. If you have a one lb thrust behind a a 100 ton mass I fail to see how that could take it beyond a few mph.
I think I see what they are saying:i.e. if you put a 1 lb thrust in pulse mode on an object and turn it on and off the object moves 10 mph, then pulse again=20 and so on,but i think at sometime when the mass and force balance out the mass will say to the force that is has exhausted it’s potential and if it wants it to go fasterit need an increase in lbs thrust..
hmm vyVY
Then you don’t understand enough about physics to participate in this discussion in a meaningful way.
no no no, this is a different point that is being dealt with aside from the discussion, now have a look at the ten mile tube post and have a meaningful discussion on that.
vyVY
btw if the gases given of by the asteroids or comet I forget which one has ice or both are considered as thrust shouldn’t they be getting faster each year? or expansion of the ice due to heat is not considered force/thrust… not a cheap shot just asking.
vyVY
here… participate with this in a meaningful way, what does your understanding of physics say about this?
Imagine a ten mile long tube north to south orientation; with one end open, in the vacuum of space. so no air is in the tube. have a fuel air mixture and light it. I guarantee you that before that expansion of gasses reaches that opening ten miles away that canister is on the move. why? because the expansion of gases expanding to the north hits the closed end of the tube. What folks are saying in here is that we have to wait until the expansion goes ten miles and exits the tube before you have movement, which is absurd!! That tube is long on its way from the north force. Its the south force vector you feel coming out the tube.. vyVY
No, it is not a different point. There are three most basic, fundamental laws of physics, Newton’s laws of motion. At various points in this discussion, you have revealed that you don’t understand (and, in fact, actively disagree with and argue against) all of them. Any discussion of more complicated systems is based on these three laws, so any attempt to discuss these systems while you still fail to understand these three laws is a waste of everyone’s time. As the past 4 pages demonstrate.
ok can you comment on this? Is this not an understanding? Is this correct?
Imagine a ten mile long tube north to south orientation; with one end open, in the vacuum of space. so no air is in the tube. have a fuel air mixture and light it. I guarantee you that before that expansion of gasses reaches that opening ten miles away that canister is on the move. why? because the expansion of gases expanding to the north hits the closed end of the tube. What folks are saying in here is that we have to wait until the expansion goes ten miles and exits the tube before you have movement, which is absurd!! That tube is long on its way from the north force. Its the south force vector you feel coming out the tube.. vyVY
No, I was telling what i was getting from the things people were explaining and what I was seeing. so you could see where I was at, so you could explain where you thought I was misapplying the laws or wrong. maybe it seemed I was against some of the ways you were applying newtons law but not the law itself. Case in point the tube in space post. That proves I was correct all along about the expansion/thrust issue. I believe it cannot be sensibly refuted. if it could have it would have been commented on by now. But no one is touching that one.It proves the theories expounded in here by the physic book thumpers wrong. It clearly are precisely proves that it is the force/expasion/agitated atoms pushing toward the front of the engine that moves the plane not the exhaust you see coming out back. that was headed that way anyway.I said it all through this post.. was ridiculed a few times and now I have proved it, and all you can say is I need to read physic books, sheesh
vyVY
Yes, the tube will move before the gas exits. The problem is, this has nothing to do with how a jet engine, a rocket engine, or even a compressed air cylinder with the valve knocked off produces thrust. For the umpteenth time: a jet engine does not involve an explosion, and does not involve an “expansion” of gases hitting the combustion chamber wall in a vacuum!
The problem is, explaining in any more detail than this is MEANINGLESS to someone who has explicitly rejected all three of Newton’s laws.
I haven’t rejected newtons laws, my illustration is correct so if newtons laws are correct they have to compliment each other.
So if it has nothing to do with how a jet,rocket engine or compressed air tank works, have I invented a new kind of engine? My example shows that for each action there is an equal and opposite reaction. tbasically for the force going to the south there is a force going to the north. The north force acts on the whats is to the north and vice versa. I came to this conclusion by observation.. going inside the engine to see what is going on, getting down to earth and dirty so to speak.. If you didn’t have you head so far up in the formula clouds you would hbeen able to come down to earth also to try and see what was actually going on inside the engine instead of relying on formulas, not that the formulas are wrong, but so yo could explain it in laymans terms.. newton OBSERVED the apple falling then tried to figure out why, he said to himself if he whittled the earth away to the size of the apple would the apple still fall to the earth or would they fall towards each other, then he worked out the formula. so he saw it in laymans terms. first. Thats all I try to do.
The reason the tube works is because of the heated agitated particles, the hotter they get the faster and farther they move. anything in their way that doesn’t have an opposite counteracting force is moved, that is why the tube moves before any exhaust is seen out the tail pipe. I put it to you the rocket engine works on the same principle, heat producing agitated particles moving at extremely high speeds in all directions, at one point the particles trying to go in the forward direction push the rocket.
To me any expansion of gases is an explosion, [An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. ] depends on what you define as extreme, combustion is a controlled explosion; controlled expansion of gasses.
I used explosion for illustrative purposes, but I can uses combustion and get the same result, which to me means heat which means agitated molecules flying in all directions. which means expansion, expansion means pressure.If you compress the air in a tank and remove all sides at once, you have expansion of gas (air) with molecules flying in all directions, this could so the same work as fire induced combustion.
so back to the ac engine: combustion is going on in the chamber, molecules flying all over the place. I assume these molecules flying all over the place in every direction are the energy produced by the combustion, you take it from there…what happens to the heated molecules?..step by step, walk me through it, where do they go what do they do and what do they act on..
vyVY
remember the molecules are flying in all directions back and forth resulting in sustained pressure on all areas of the chamber… if you want to get technical there is another turbine system after the combustion chamber that taps some air energy (like a dam turbine taping the water energy)on its way out to turn the front turbine, not necessary for this but I mentioned it all the same
vyVY
Okay, let’s back up. The reason we ended up in this discussion is your claim that, in a jet engine, there is “a combustion emanating from a central point”. You seem to have a view that half of the “thrust” goes towards the front of the engine, where it collides with the wall and pushes the engine forward, and half of the thrust is “wasted” because it goes the other way, straight out the back.
You are correct in that some of the thrust of a rocket comes from the pressure of the gas molecules hitting the forward combustion chamber wall. You are incorrect in your claim that anything about the gas that initially expands out the back of the nozzle is “wasted”. That was how this whole discussion got started, and you’re right, I was too hasty. We can have a reasonable discussion about a jet engine in the context of your tube.
Your understanding would be correct if we were talking about an explosion of macroscopic particles (i.e. chunks of debris), which all move outwards in pretty much a straight line from the source of the explosion. If you were trying to drive your tube through space by somehow creating explosions that released only a spray of small metal BB pellets, instead of a gas, your intuitive understanding would be correct. Half those chunks of metal would have some component in the forward direction and collide with the front of the tube, driving it forward, and the other half would have a component in the backward direction, and go straight out the back without doing jack shit to the velocity of the tube.
However, a gas is not like that, unless it is a very, very low density gas. Gas molecules are so small, and there are so many of them, that they are constantly colliding with each other and changing direction. Only a very few gas molecules at the outer edge of the expanding cloud are moving in a straight line - the others are bouncing around, colliding with each other, and only moving outwards on average, when you consider the averaged motion of all the quadrillions of gas molecules together.
There is a term for this in physics, it is called the mean free path - the average distance that a gas molecule will travel before colliding with another gas molecule and changing direction. At 1 atmosphere pressure, this is approximately 0.00006 mm. At higher than atmospheric pressure, such as inside the combustion chamber of a jet engine or rocket, it is yet smaller. Even at 1 atmosphere, a 1-foot-wide nozzle has approximately 500,000 mean free paths across it - meaning a gas molecule would on average collide and (essentially randomly) change direction 500,000 times before traveling across that 1-foot distance.
As a result, gas molecules can transfer energy to and from each other in a way that an expanding field of macroscopic objects can not. Gas molecules are constantly colliding with each other and distributing energy and pressure throughout the gas - an expanding field of metal BBs is not.
So, in a rocket driven by an explosion in the center, yes, you will have two clouds of gas moving in opposite directions - on average. But inside, the molecules are constantly colliding and bouncing and moving every which way.
So, when the gas hits the forward wall of the combustion chamber, yes, it exerts a pressure and drives the rocket forward. But then what happens? The gas molecules bounce off the forward wall, and are now heading in the backward direction. The reason the rocket/jet engine/whatever continues to experience a forward thrust is that those molecules move only 0.00006 mm (on average) backward, before colliding with some other molecule, and being reflected back into the forward wall of the chamber, like a billiard ball. And then the molecule that that molecule colliding with gets reflected in the backward direction, and collides with another molecule, and so forth. This process repeats billions and billions of times (actually more like a billion^2 times), and over time, it transfers energy from the heated gas molecules to the forward wall of the rocket. On average, you end up with a situation in which the rocket is moving in the forward direction, and the average velocity of the gas molecules has a bias in the backward direction (this means that, even though the velocity of any single molecule could be pointing in any direction, if you pick one at random, you are slightly more likely to find a particle that is going backward than forwards).
So, what is the point? The point is that, because this cloud of molecules is a gas, in which the molecules are constantly colliding and transferring energy and moving macroscopically only on average, not a bunch of metal BB’s flying in straight lines from a central point, even the gas which is moving away from the central point on average can transfer energy to the forward wall of the combustion chamber! And so the motion of the gas moving in the “backward” direction is not wasted, but in fact, pretty much contributes just as much thrust as the gas initially moving in the forward direction.