How can a spaceship move in the vac of space?

[Triumph]

Originally posted by: funboy42

Originally posted by: Linflas

Originally posted by: funboy42

Originally posted by: LeadMagnet
The rocket is pushing against the exhaust itself

But in order to push on the exhaust itself would the exhaust have to has something to resist it from moving? Meaning there would have to me some sort of atmosphere to hold the exhaust back for the rocket to propell off of it no?

No that is not how it works. Here have a look.

I read that before trying to find how they work in space. I know newtons law but if your in a vacuum with nothing to push off of what makes it work. Its like taking a fan into space. You can turn it on and the blades will spin like crazy but there isnt any air to push to make you move and your just going to sit there. A rocket to move has to push against something to move. To get off the ground it pushes off the earth then the atmosphere to achieve lift off. But in a vacuum there is no air or atmosphere to push off of so when the rocket fires it would be like my fan. Its blowing but nothing there to make it move. And I know it works how else would they be moving around but from what I know (which isnt much) it doesnt make sense to me.

Or are they on the bleeding edge of the earth where there is some atmosphere where they are able to still move?

NO it does not "push of the ground" to achieve liftoff. That is not how a rocket works at all. I don't know if I can explain it without pictures, but imagine a sealed rocket motor that is burning, thus there is very high pressure inside. Pressure is force/unit area, on each internal face the pressure is pushing on that face. Now open up one end. Suddenly you have an imbalance of force because there is no face to put pressure on. Because there is still a face on the (forward) inside end of the motor, the pressure pushes on that side and the rocket moves in that direction.

Because I'm such a nerd, here is a picture

 

[Shadowknight]

Originally posted by: Linflas

III. For every action there is an equal and opposite reaction.

Not really. If you post certain opinions on message boards, whether it be about Bush, Abortion, or what you think of Spider-man's new costume, there will be a more vicious and unrelenting side that needs happy pills and or therapy.

 

[ahurtt]

Originally posted by: funboy42

Originally posted by: Linflas

Originally posted by: funboy42

Originally posted by: LeadMagnet
The rocket is pushing against the exhaust itself

But in order to push on the exhaust itself would the exhaust have to has something to resist it from moving? Meaning there would have to me some sort of atmosphere to hold the exhaust back for the rocket to propell off of it no?

No that is not how it works. Here have a look.

I read that before trying to find how they work in space. I know newtons law but if your in a vacuum with nothing to push off of what makes it work. Its like taking a fan into space. You can turn it on and the blades will spin like crazy but there isnt any air to push to make you move and your just going to sit there. A rocket to move has to push against something to move. To get off the ground it pushes off the earth then the atmosphere to achieve lift off. But in a vacuum there is no air or atmosphere to push off of so when the rocket fires it would be like my fan. Its blowing but nothing there to make it move. And I know it works how else would they be moving around but from what I know (which isnt much) it doesnt make sense to me.

Or are they on the bleeding edge of the earth where there is some atmosphere where they are able to still move?

If you took a fan in space and powered it on (say it's battery powered and has no cord to get in the way), the fan housing would begin revolving around the fan blades in the opposite direction from the spin of the blades. . .assuming that the fan were just floating free and not affixed to any surface. If the fan were also perfectly weighted and balanced, the blades and the housing would spin in opposite directions at equal speeds. The housing and blades would spin at a speed that is about half of how fast the blades would spin if the housing were affixed to some solid object. So yes, the fan would move, just not in the way you are thinking of. For the same reason the rockets can push spacecraft through space. . .

 

[raptor13]

Originally posted by: ahurtt

Originally posted by: funboy42

Originally posted by: Linflas

Originally posted by: funboy42

Originally posted by: LeadMagnet
The rocket is pushing against the exhaust itself

But in order to push on the exhaust itself would the exhaust have to has something to resist it from moving? Meaning there would have to me some sort of atmosphere to hold the exhaust back for the rocket to propell off of it no?

No that is not how it works. Here have a look.

I read that before trying to find how they work in space. I know newtons law but if your in a vacuum with nothing to push off of what makes it work. Its like taking a fan into space. You can turn it on and the blades will spin like crazy but there isnt any air to push to make you move and your just going to sit there. A rocket to move has to push against something to move. To get off the ground it pushes off the earth then the atmosphere to achieve lift off. But in a vacuum there is no air or atmosphere to push off of so when the rocket fires it would be like my fan. Its blowing but nothing there to make it move. And I know it works how else would they be moving around but from what I know (which isnt much) it doesnt make sense to me.

Or are they on the bleeding edge of the earth where there is some atmosphere where they are able to still move?

If you took a fan in space and powered it on (say it's battery powered and has no cord to get in the way), the fan housing would begin revolving around the fan blades in the opposite direction from the spin of the blades. . .assuming that the fan were just floating free and not affixed to any surface. If the fan were also perfectly weighted and balanced, the blades and the housing would spin in opposite directions at equal speeds. The housing and blades would spin at a speed that is about half of how fast the blades would spin if the housing were affixed to some solid object. So yes, the fan would move, just not in the way you are thinking of. For the same reason the rockets can push spacecraft through space. . .

The blades only spin half as fast? That all depends on your point of view, mate. 😉

 

[Connoisseur]

Throw a ball on earth, your body automatically reacts by tensing your muscles and counteracting the opposing force of the ball. Throw a ball in outer space with no footing and you'll get pushed back with the same force with which you threw the ball. It's got nothing to do with air. If action/reaction is a bit hard to swallow, don't worry about it. Newton didn't understand it either. He just wrote some equations to describe the laws.

 

[miniMUNCH]

take a physics class or read a intro physics book.

 

[funboy6942]

Originally posted by: funboy42
OK some of the replies do make sense and I think I have a handle on it. It was just one of thoes questions I been wondering about and needed lamens terms explained to me for me to understand it.
Thnaks!!!!

 

[FoBoT]

oars

you have to use oars in outside space

 

[aircooled]

How can a spaceship move in the vac of space?

They are traveling in the Oreck 8 pound vacuum of space.

 

[Kadarin]

It burns phlostigon in order to push against the ether. Duh!

 

[silverpig]

Originally posted by: Armitage
Physics 101 - 1st week even.

Conservation of Momentum - here's a start: http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l2b.html

m1 * dv1 = m2 * dv2

m1: mass of rocket
dv1: rocket velocity
m2: mass of rocket exhaust
dv2: velocity of rocket exhaust

A rocket engine sends some mass out the back at a very velocity. By the equation above, the rocket moves in the opposite direction with a corrosponding velicity such that momentum is conserved.

Except it's actually

m1*dv1 + dm1*v1 = m2*dv2 + dm2*v2

 

[slpaulson]

I'd guess they work by conservation of momentum...

edit: nevermind, it's covered above.

 

[Armitage]

Originally posted by: silverpig

Originally posted by: Armitage
Physics 101 - 1st week even.

Conservation of Momentum - here's a start: http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l2b.html

m1 * dv1 = m2 * dv2

m1: mass of rocket
dv1: rocket velocity
m2: mass of rocket exhaust
dv2: velocity of rocket exhaust

A rocket engine sends some mass out the back at a very velocity. By the equation above, the rocket moves in the opposite direction with a corrosponding velicity such that momentum is conserved.

Except it's actually

m1*dv1 + dm1*v1 = m2*dv2 + dm2*v2

shrug - yep, but this guys is having trouble with Newton's 1st to begin with so I didn't want to complicate things. Mine is correct for the case where both the rocket & the exhaust are initially at rest (v1 = v2 = 0) - such as releasing a stationary bowling ball and a marble with a compressed spring between them...

0||||o
0\/\/\/\/o

 

[mordantmonkey]

i think he's confusing rockets with gas-turbine engines, which do rely on atmosphere to provide thrust.

 

[Armitage]

Originally posted by: mordantmonkey
i think he's confusing rockets with gas-turbine engines, which do rely on atmosphere to provide thrust.

Well ... they rely on the atmosphere to provide the working fluid (and oxydizer for the fuel). But the thrust is provided by the exact same mechanism ... a jet engine does not move forward by "pushing against" the atmosphere.

 

[imported_electron]

Originally posted by: funboy42

Originally posted by: LeadMagnet
The rocket is pushing against the exhaust itself

But in order to push on the exhaust itself would the exhaust have to has something to resist it from moving? Meaning there would have to me some sort of atmosphere to hold the exhaust back for the rocket to propell off of it no?

Yes the exhaust would have to have something to resist it from moving, that is called inertia.

 

[Eeezee]

Quote for you:

That Professor Goddard, with his 'chair' in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than vacuum against which to react--to say that would be absurd. Of course, he only seems to lack the knowledge ladled out daily in high schools."

--New York Times, January 13 1920

This is a quote from the New York Times explaining that space travel can never happen. It was published Jan 13, 1920.

You, sir, are 85 years behind your time 😛

Here's another fun quote

"...an editorial feature of the New York Times dismissed the notion that a rocket could function in a vacuum and commented on the dieas of Robert H. Goddard...Further investigation and experimentation have confirmed the findings of Issac Newton in the 17th Century, and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."

--New York Times, July 17 1969

One way of making a rocket ship move forward is by simply throwing something out the back. This is a momentum concept. Momentum is always conserved, so if you throw a heavy brick out the back of a rocketship, the rocketship will gain some velocity. In other words, the rocketship is experiencing a push forward because exhaust is leaving the ship in the opposite direction (so it's like a man is throwing particles out of the ship). You don't need an atmosphere to experience a push. An atmosphere is not special

I'm surprised you don't have any qualms with gravity. How can action occur at a distance? Nothing is physically pulling planets together or keeping us in orbit. It's all action at a distance.

 

[Eeezee]

Also, space is not a perfect vacuum

 

[PHiuR]

Originally posted by: Eeezee
Also, space is not a perfect vacuum

this is

 

[spidey07]

to make this overly simply (and it's the exact same pricniple of a rocket)..

1) take ballon
2) inflate
3) let go of ballon
4) ballon flies (it's not pushing against anything, it is being acted upon by a force...)

you have in essence created a rocket

 

[Goosemaster]

Originally posted by: Eeezee
Also, space is not a perfect vacuum

A dyson is however:heart:

 

[Armitage]

Originally posted by: Eeezee
Quote for you:

That Professor Goddard, with his 'chair' in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than vacuum against which to react--to say that would be absurd. Of course, he only seems to lack the knowledge ladled out daily in high schools."

--New York Times, January 13 1920

This is a quote from the New York Times explaining that space travel can never happen. It was published Jan 13, 1920.

You, sir, are 85 years behind your time 😛

Here's another fun quote

"...an editorial feature of the New York Times dismissed the notion that a rocket could function in a vacuum and commented on the dieas of Robert H. Goddard...Further investigation and experimentation have confirmed the findings of Issac Newton in the 17th Century, and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."

--New York Times, July 17 1969

In case anybody missed the significance of that date, this was the day after the Apollo 11 flight lifted off. 3 days later man first walked on the moon.

Of course, we had been - against all logic - flying rockets in space for over a decade at that point 😛

One way of making a rocket ship move forward is by simply throwing something out the back. This is a momentum concept. Momentum is always conserved, so if you throw a heavy brick out the back of a rocketship, the rocketship will gain some velocity. In other words, the rocketship is experiencing a push forward because exhaust is leaving the ship in the opposite direction (so it's like a man is throwing particles out of the ship). You don't need an atmosphere to experience a push. An atmosphere is not special

I'm surprised you don't have any qualms with gravity. How can action occur at a distance? Nothing is physically pulling planets together or keeping us in orbit. It's all action at a distance.

 

[3chordcharlie]

No atmosphere needed for a rocket - I'm pretty sure one is needed for a jet though, I think a simple analogy is to think of a small boat - you can make the boat move back and forth by moving yourself in the boat, throw something off the back, and you will actually manage some momentum. This is like a rocket.

You could also paddle the boat - your paddle moves through the water, so you send some water moving backwards, but there is also resistance to push against; this is what a jet does: throws air very hard, and gets thrust based on the resistance provided by the air. basically paddling, but with a turbine.

 

[silverpig]

Originally posted by: Armitage

Originally posted by: silverpig

Originally posted by: Armitage
Physics 101 - 1st week even.

Conservation of Momentum - here's a start: http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l2b.html

m1 * dv1 = m2 * dv2

m1: mass of rocket
dv1: rocket velocity
m2: mass of rocket exhaust
dv2: velocity of rocket exhaust

A rocket engine sends some mass out the back at a very velocity. By the equation above, the rocket moves in the opposite direction with a corrosponding velicity such that momentum is conserved.

Except it's actually

m1*dv1 + dm1*v1 = m2*dv2 + dm2*v2

shrug - yep, but this guys is having trouble with Newton's 1st to begin with so I didn't want to complicate things. Mine is correct for the case where both the rocket & the exhaust are initially at rest (v1 = v2 = 0) - such as releasing a stationary bowling ball and a marble with a compressed spring between them...

0||||o
0\/\/\/\/o

No it's not. You have to include the dm terms as the mass of the rocket changes at it burns and expels fuel. The apollo lander sure was less massive than the Saturn V 🙂

 

[Armitage]

Originally posted by: silverpig

Originally posted by: Armitage

Originally posted by: silverpig

Originally posted by: Armitage
Physics 101 - 1st week even.

Conservation of Momentum - here's a start: http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l2b.html

m1 * dv1 = m2 * dv2

m1: mass of rocket
dv1: rocket velocity
m2: mass of rocket exhaust
dv2: velocity of rocket exhaust

A rocket engine sends some mass out the back at a very velocity. By the equation above, the rocket moves in the opposite direction with a corrosponding velicity such that momentum is conserved.

Except it's actually

m1*dv1 + dm1*v1 = m2*dv2 + dm2*v2

shrug - yep, but this guys is having trouble with Newton's 1st to begin with so I didn't want to complicate things. Mine is correct for the case where both the rocket & the exhaust are initially at rest (v1 = v2 = 0) - such as releasing a stationary bowling ball and a marble with a compressed spring between them...

0||||o
0\/\/\/\/o

No it's not. You have to include the dm terms as the mass of the rocket changes at it burns and expels fuel. The apollo lander sure was less massive than the Saturn V 🙂

I guess I should state my assumptions more clearly. Yes, for the full proper treatment you need to consider the change in mass of the rocket. That's why you have to throttle back the shuttle engines at some point so you don't exceed your acceleration limits.

What I'm describing is a single instantaneous event - the first molecule to leave the nozzle if you like 😛 Simply to demonstrate conservation of momentum. Integrate that over time to get the rocket equation.