Again: HOW IS THE GAS ACCELERATED?
Apply Newton's laws of motion to the gas, initially in the rocket at rest relative to the rocket.
Initially in the rocket at rest relative to the rocket?
Is that the same moment when the rocket is still at rest relative to the earth, also?
I answered all your questions, and if you think i didn't, then why don't you enlighten us (finally), instead of endlessly regurgitating your same stupid questions?
Once again, just for you :Thrust=force=mass*acceleration.
Thrust = (mass flow rate) × (exhaust velocity)
NASA SAYS :
"The physics involved in the generation of thrust is introduced in middle school and studied in some detail in high school and college. To accelerate the gas, we have to expend energy. The energy is generated as heat by the combustion of some fuel."
According to Jack, generated energy (as heat by the combustion) is the force which produces another force (thrust) which is (mass (flow (rate) * (exhaust velocity).
The first force (combustion-expansion-chemical reaction) forces one part of the second force (mass flow rate) to accelerate (which is another part of the second force).
So, we have the first force (chemical reaction) and the second force (thrust).
Now, according to Jack's logic, the second force is not the whole force, but only one part of the second force (mass (flow rate)).
In order to get the entire force (thrust) we need the first force (chemical reaction) which is going to accelerate one part of the first force (mass).
Now, according to Jack, the first force (chemical reaction) is actual-real force, and thrust is only one part of what it really is (mass (flow rate)).
This is how Jack invented something (first force) that can artificially separate thrust (which is actually just one part (mass (flow rate)) of what it really is : (mass flow rate) × (exhaust velocity)) from a rocket.
So, the first body is a rocket, second body is a thrust (which is actually just one part (mass (flow rate)) of what it really is : (mass flow rate) × (exhaust velocity), and the force is actually the first force (chemical reaction) which accelerates second body (thrust) so that we can finally get thrust in it's integrality.
This is an interesting theory (which eventually boils down to nothing more than meaningless wordplay), but it is plainly wrong, that is to say : just one among many classical examples of notorious Jack's stupidities.
Newton's Third Law - Identifying Action and Reaction Force PairsA force is a push or a pull that acts upon an object as a results of its
interaction with
another object. Forces result from
interactions!
"When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body."
Jack still hasn't watched this video :
https://www.dailymotion.com/video/x7ga9h2No, the “second body” isn't the gases...in a rocket launch...the rocket (engine) is the “first body” applying force (expelled gases= thrust= mass flow rate* exhaust velocity) to a second body (ground, then atmosphere).. which “pushes back” with equal and opposite force.. on the first body (rocket) forcing it to go up..
What happens in a REAL and INFINITE vacuum, where there is no “second body” to act upon???
THE ROCKET (ENGINE) = FIRST BODY
THRUST FORCE = EXPELLED GASSES
GROUND/ATMOSPHERE =
SECOND BODYThe gas cannot push the ship with the nozzle closed because gas trapped in the combustion chamber does no work but if you open the nozzle all the gas exits immediately before it can push against the ship. Therefore you cannot use gas in the vacuum to power a rocket ship.
This force pushing a rocket cannot be pushing on the inside of the rocket any more than you can push with your feet upwards against the inside of a cardboard box you are within to stop it from falling from a height. It sounds absurd but that is what NASA claims happens in a rocket.An object sitting on the ground can only move upwards if it is pushed from underneath or lifted from the side/top. Since we know rockets are not lifted , they must be pushed. Therefore the gasses underneath the rocket must be pushing it up and off the launchpad.
An object moving straight up into the air will eventually be pulled back down by gravity unless it is continuously pushed from underneath or pulled from the top/side by a force greater than gravity.
The Expansion produces
THRUST FORCE!
What law disables rockets (via expansion) from doing any useful work in a vacuum?
Free expansion!What makes "the difference" between the Expansion and Free expansion?
Density of air/vacuum! Why?
Resistance!What it means?
It means that there is resistance in the air because the air is dense, hence : the air is the second body!On the other hand, there is no resistance in a vacuum, hence : the second body is missing!3. Jack, have you ever seen this :BULLSHIT VS
COMMON SENSE BULLSHIT :
An airplane propeller DOES push against the air and in so doing it DOES impart a reactive force to the plane because the prop is a solid object CONNECTED to the plane.
Rocket exhaust isn’t connected to the rocket so it can’t function as a pushing medium to the rocket as a propeller does.
Rockets move by creating an imbalance of forces within the rocket motor causing more internal pressure in the forward direction and very little internal pressure rearward due to the opening of the rocket nozzle. There is also a secondary forward thrust caused by Newton’s 3rd law as regards the rearward ejection of mass.
That is how rocket thrust works. The continued expansion of gasses caused by burning high energy fuel builds up pressure but the pressure is always lower at the rear of the rocket motor due to the open nozzle. The higher pressure in the forward part of the motor maintains an imbalance of forces so the rocket continues to move as long as fuel is burned.
In addition to the above force there is also some thrust caused by rearward ejection of mass (the exhaust) in accordance with Newton’s 3rd Law.BULLSHIT VS
COMMON SENSE COMMON SENSE :
I fear we are now arguing semantics instead of physics.
To save time, I will tell you how I interpret Newtons 3 Laws of Motion. If you disagree then there is no longer a reason to continue this thread as we differ on basic laws of physics which won’t be resolved here. If you agree with me, then there is much to discuss.
Let’s start with Newtons 3 Laws of Motion.
Fist Law: For an object to remain as it is, either moving or not, the sum of the forces on it are zero.
Sigma F = 0
Second Law: For a body to accelerate, there must be a force on it.
F = ma
Third Law: For every force in one direction, there is an equal force in the opposite direction.
F1 = – F2 or F1 + F2 = 0
Notice how all of Newtons Laws of Motion contain the term ‘force’. Newton used the term ‘force’ to explain how objects are pushed and pulled in our universe.
This is how I see Newtons 3rd Law applied to rockets flying through our atmosphere:
If a rocket is moving through the air at 17,000 mph in a southwesterly direction, then there must be a force in the northeasterly direction also going 17,000 mph, which is the force produced by the jet engine exhaust coming out of the back of the rocket.
The way you are explaining it, is that molecules hitting inside a chamber are moving the rocket forward, AND the rocket is moving forward. You did mention the perhaps the exhaust might move it forward also somewhat, but Newtons 3rd Law says the forward motion MUST be equal to the thrust only out the back because of the ‘opposite’ direction part of the law.
You can’t have two positive forces. F1 + F2 would then be greater than zero, and that defies Newtons 3rd Law. My point is the exhaust out the back is not the minor part, it is the major part of the force. Newtons 3rd law says it has to be.4. Jack, have you ever seen this :
So you go and find the "As we shall see latter
(sic), maximum thrust occurs when
Pe=Pa" and find out what it means.
[/quote]
Let's try once again :1. When a rocket's combustion chamber is filled with accelerated gas opening the nozzle to expel the gasses into the vacuum of space does not generate a force against the ship. This is due to the principle of
free expansion.
2. No amount of combustion or pressure inside the space ship can move the ship until that combustive force or pressure is exchanged with some object, entity, or field
outside of the ship (a space ship is a
closed system).
3. Based on 1 and 2 there is no way to move the ship by releasing gas and no way to move the ship by keeping the gas inside. A space ship cannot generate force with a gas based propulsion system. Space rockets are the stuff of fantasies not science or physics.
4. Any liquid exposed to a vacuum is immediately converted to gas and any gas is immediately spread out into the void. So any combustion would have to take place in a sealed container and hence not in a vacuum in the strict sense.
5. Contrary to known rocket's trajectories, they need to end up going seven miles per second away from the center of gravity (center of gravity = center of the earth)! (see
reply #270)
Regarding the possibility of opening one side of a container, exposing it to the vacuum, while combusting gasses inside the container. In this case we have to consider that combustion can't occur anywhere near the opening because any liquids in that area are being instantly converted to gas by the vacuum and spread out into the void via
free expansion. When combustion occurs at the far side of the container
the force is going to push the remaining liquid out before it can be combusted. This seems like a terribly inefficient use of fuel as the combustion itself is forcing unspent fuel into space.
Another problem is that gas enters a vacuum at an average speed of about
2,000 meters a second. A 25 meter long Saturn 5 stage 2 fuel tank with over 1,000,000 liters of fuel would have it's contents drained in about 1/100 of a second if exposed to the vacuum of space.
Well, consider this: no honest scientists will deny that, when opening a valve between two containers (one containing air at high pressure - and the other only vacuum) the pressures in the two containers will equalize in a fraction of a second, the vacuum container 'sucking' the air to itself with tremendous, almost explosive force.
Imagine now the high pressure emitted by any rocket from its (always open) nozzle. As it enters the vacuum of outer space, the very same - almost explosively rapid - pressure equalization is bound to occur. The rocket will be emptied of all of its pressurized fuel in a flash - by the overwhelmingly superior power of the vacuum itself. No matter how powerful the rocket (propelled by any fuel known to man / and designed to perform in our 0,001 atmosphere) - the very laws of physics will not allow it to ascend any further into the void of space. It will haplessly tumble back to Earth.
In Summary1. Without free expansion the rocket exhaust will push against space. And off we go!
2. Objects don't accelerate unless they exchange energy with some other object/field. There are no objects or fields in space (I regard them to be so small/weak as to be virtually non-existent).
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