What does a rocket push against in space?

a reply to: sapien82

originally posted by: buddha

But in the vacuum of space you have Nothing to push against.

Yeah, you're "pushing" against the rockets own "inertia."

A smart fella called Einstein claimed that "inertial mass" and "gravitational mass" are indistinguishable from one another. So, the same "mass" that causes the rocket to "feel" the planetary gravitation, also produces "resistance" to acceleration when you try to "push" that rocket faster way out in space where the gravitational forces of all the bodies in the universe is small.

I stated in a previous post in this thread that a rocket engine produces thrust mainly because of the pressure difference between the to sides of the combustion chamber. One side high pressure and the other where the opening is low pressure with thrust being in the direction of the high pressure side.

In this post I am making a clarification. The low pressure side has to be at 0 or negative pressure for the thrust to occur.

For those attempting to design an inertial propulsion engine must take this concept into consideration.

Rockets don't work in space.

www.youtube.com...

To me the cool part is how the they calculated the thrust along with the vacuum of space. Meaning, they use MORE thrust than the vacuum of space, right?

Otherwise it would not push.

Right?

a reply to: buddha

What does a rocket push against in space?

Itself.

Second, and third line.............

a reply to: All Seeing Eye

no it doesn't

a reply to: buddha

You could toss rocks out the back and cause movement.

a reply to: Xeven

how is that the same as gas moving due to pressure gradient force?

a reply to: NicSign
Well it is not “same” but still


The pressure-gradient force is the force that results when there is a difference in pressure across a surface.

I would transfer the pressure of the rock through my feet onto surface of the craft as I toss it. I am not a scientist or expert but I can imagine the interaction in my mind.

I imagine there would also be some additional pressure from the energy I use to toss the rock.

Another thread despite the initial premise that I have learnt from, my own simple take is that we dont really fly in space like anything seen in movies, we have to hit escape velocity from the nearest gravity field, so when we WENT to the moon it was more about plotting a path through space until the moons gravity grabbed the capsule, its not elegant like in movies with people sat down and smoking cigars



It is more of a tumble drier expierince constant pitching, yawing and tumbling, this then needs the pilot to orientate the capsule with minor increments of thrust so the vehicle is level with the surface of the moon, it then basically falls to the moon surface and is then slowed down enough to land, true genius of Maths and education got us there not some elaborate space vehicle.

To the OP there has been enough honest, trustworthy and reliable information provided to your question, has this thread changed your mind, helped you learn I hope so, I did

originally posted by: Xeven
a reply to: NicSign
Well it is not “same” but still
The pressure-gradient force is the force that results when there is a difference in pressure across a surface.
I would transfer the pressure of the rock through my feet onto surface of the craft as I toss it. I am not a scientist or expert but I can imagine the interaction in my mind.
I imagine there would also be some additional pressure from the energy I use to toss the rock.

Yes. And as I mentioned on another thread, a similar thought experiment would be if you threw objects while standing on a skateboard.

If you threw a 15-pound iron ball that's the size of a softball (say about 5 inches in diameter) with enough force that in landed 5 feet in front of you, your skateboard would go the opposite direction a certain distance (Newtons' "every action has an opposite and equal reaction").

Now, if I did the same with a 20-inch diameter inflated beach ball that might weigh only a few ounces, it would take me far less force to throw it 5 feet, so the skateboard would move in the opposite direction a shorter distance than with the iron ball.

Some people on the YouTubes claim that a rocket needs air to push against, but the beach ball (having a much lager diameter and cross-sectional area) would be pushing against the air far greater when I threw it than the smaller iron ball. So it the "rocket pushes against air" people were right, then the skateboard should move more when the beach ball is thrown.

But it doesn't, so those people are wrong.

Manned Maneuvering Unit

The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984. The MMU allowed the astronauts to perform untethered EVA spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2.

Gaseous nitrogen was used as the propellant for the MMU. Two aluminium tanks with Kevlar wrappings contained 5.9 kilograms of nitrogen each, enough propellant for a six-hour EVA depending on the amount of maneuvering done. Typical MMU velocity capability was about 80 feet per second (25 m/s).

There were 24 nozzle thrusters placed at different locations on the MMU. To operate the propulsion system, the astronaut used their fingertips to manipulate hand controllers at the ends of the MMU's two arms. The right controller produced rotational acceleration for roll, pitch, and yaw. The left controller produced translational acceleration for moving forward-back, up-down, and left-right. Coordination of the two controllers produced intricate movements in the unit. Once a desired orientation was achieved, the astronaut could engage an automatic attitude-hold function that maintained the inertial attitude of the unit in flight. This freed both hands for work.

Link

a reply to: Xeven

how to you measure the pressure difference between your hand and the rock? lol. When you say you're not a scientist, you mean it.

a reply to: UpIsNowDown

no change of mind until an equal and opposite force from gas movement due to pressure gradient force is proven.

originally posted by: NicSign
a reply to: Xeven

how to you measure the pressure difference between your hand and the rock? lol. When you say you're not a scientist, you mean it.

Still trolling with this nonsense?

a reply to: NicSign

Actually they do!!
Give it up.

Well, the American moon landings used rockets, they worked, thats all I need to know, I'll leave the rest to rocket scientists.

a reply to: buddha

Ummm....if the gas the rocket just pushed out the back is going the same speed as the gas it is pushing out now, they will never touch.

Rockets do not work by pushing against something. The rapidly expanding ignited fuel exiting the rocket creates an equal and opposite action on the rocket itself. Newton's Third Law. Gas goes out the back - thrust is forward.