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Yes you did sort of answer your own question. That's actually in interesting and relevant question which has been brought up recently in the context of EM drives, where the thrust is provided by photons, which have no rest mass therefore there is no "reaction mass". There is apparently some question about whether existing theory can adequately explain some recent experimental results in that regard, so it should be interesting to watch the developments on that topic to see the ultimate resolution.
originally posted by: eManym
What force is being exerted on the vehicle body to make it move?
Isaac Newton stated in his third law of motion that "for every action there is an equal and opposite reaction." It is upon this principle that a rocket operates. Propellants are combined in a combustion chamber where they chemically react to form hot gases which are then accelerated and ejected at high velocity through a nozzle, thereby imparting momentum to the engine. The thrust force of a rocket motor is the reaction experienced by the motor structure due to ejection of the high velocity matter. This is the same phenomenon which pushes a garden hose backward as water flows from the nozzle, or makes a gun recoil when fired.
a combustion chamber with an opening, the nozzle, through which gas can escape. The pressure distribution within the chamber is asymmetric; that is, inside the chamber the pressure varies little, but near the nozzle it decreases somewhat. The force due to gas pressure on the bottom of the chamber is not compensated for from the outside. The resultant force F due to the internal and external pressure difference, the thrust, is opposite to the direction of the gas jet. It pushes the chamber upwards.
To create high speed exhaust gases, the necessary high temperatures and pressures of combustion are obtained by using a very energetic fuel and by having the molecular weight of the exhaust gases as low as possible. It is also necessary to reduce the pressure of the gas as much as possible inside the nozzle by creating a large section ratio. The section ratio, or expansion ratio, is defined as the area of the exit Ae divided by the area of the throat At.
The thrust F is the resultant of the forces due to the pressures exerted on the inner and outer walls by the combustion gases and the surrounding atmosphere, taking the boundary between the inner and outer surfaces as the cross section of the exit of the nozzle. As we shall see in the next section, applying the principle of the conservation of momentum gives
where q is the rate of the ejected mass flow, Pa the pressure of the ambient atmosphere, Pe the pressure of the exhaust gases and Ve their ejection speed. Thrust is specified either at sea level or in a vacuum.
Not sure how it helps you to cite an experiment which contradicts your model?
originally posted by: eManym
They hit the Moon's surface at the same time. I say that objects don't fall at the same speed.
I don't follow that at all. Is there any real world example of what you're talking about? You already mentioned the moon, and compared to the Earth, it's lower gravity and we can see things fall slower on the moon which again contradicts your hypothesis.
If the force of gravity is greater than the force that is holding a mass together than the mass will have a slower fall rate. In a very high force of gravity environment masses will fall at a slower rate than masses in a lower gravity environment.
near a black hole (assuming that there is no nearby matter), objects would actually be destroyed and people killed by the tidal forces, because there is no radiation. Moreover, a black hole has no surface to stop a fall. As an object falls into a black hole, the tidal forces increase to infinity, so nothing can resist them. Thus, the infalling object is stretched into a thin strip of matter. Close to the singularity, the tidal forces even tear apart molecules.
Not necessarily true. You will actually see yourself falling extremely slowly as time ticks very very fast there, whereas to an external observer would appear to fall very fast.
originally posted by: Arbitrageur
a reply to: eManym
I repeat: "Is there any real world example of what you're talking about?"
There is "spaghettification" of objects falling into a black hole, but they would only appear to fall slowly to an external observer due to time dilation. If you were falling into a black hole, you would see yourself falling very fast, until you were killed by spaghettification from the immense gravity.
originally posted by: eManym
The Earth doesn't have a gravity field that exceeds the force that holds a mass together i.e. the binding force. I am talking about a force of gravity that is greater than the binding force holding the mass together.
originally posted by: dragonridr
You confused me with the gravity vs gravity thing at the end. When something crosses the roche limit it isnt gravity vs gravity its gravity vs centrifugal force. Its a difference in tidal forces that rips things apart.
Since tidal forces overwhelm the gravity that might hold the satellite together within the Roche limit, no large satellite can gravitationally coalesce out of smaller particles within that limit. Indeed, almost all known planetary rings are located within their Roche limit
Some real satellites, both natural and artificial, can orbit within their Roche limits because they are held together by forces other than gravitation.
Jupiter's moon Metis and Saturn's moon Pan are examples of such satellites, which hold together because of their tensile strength
Note the aforementioned rings. That's what you get inside the Roche limit.
im unclear if you believe gravity can separate individual atoms at the roche limit
I think he's right to an extent, but I don't think we are near the end of that fundamental discovery. Your point that we will reach limitations on the size of particle accelerators we are economically willing to build is valid. There is a possibility that cosmic rays with much higher energies than any particle accelerator produces might be utilized even more than we are already doing. There is a limited, expensive experiment for cosmic ray observation on the ISS, but much larger and even more expensive space observation apparatus is conceivable. We do have observation arrays for cosmic rays on the ground, but those are less likely to lead to fundamental new discoveries than observations in space before all the atmospheric particle showers are created.
The age in which we live is the age in which we are discovering the fundamental laws of nature, and that day will never come again. It is very exciting, it is marvelous, but this excitement will have to go. Of course in the future there will be other interests. There will be the interest of the connection of one level of phenomena to another—phenomena in biology and so on, or, if you are talking about exploration, exploring other planets, but there will not be the same things we are doing now.
Since the topic of this thread is "Ask any question you want about Physics", are you asking a question? I couldn't find one easily and I don't really understand the topic of your post. Did you mean to post that in a different thread?
originally posted by: cloaked4u
I'm just guessing here, i barely made it thru geometry in school , so don't bash me to hard.
originally posted by: Diablos
Building on my post earlier in the thread, what do you guys make of this apparently controversial op-ed op-ed by John Horgan:
Gr owing time lag for nobels portend the end of fundamental discoveries in physics.
From the looks of it, he's mainly talking about particle physics here. In condensed matter, plasma, and AMO (Atomic, molecular, optical), obviously this would not apply. But it seems to me experimental HEP has a very dire future, and that the next generation accelerators (assuming they are built) will be the last once they turn up nothing.