What Will Happen to a Fan in Space?

[amey_naik2812]

if a fan with a battery is placed in space outside Earth and if it is switched on...
then what will happen?
will the fan go ahead, behind or will it remain at the same position?

 

[Jack21222]

I'm curious as to what your intuition tells you. What do you think will happen, and why?

Also, what do you think makes propellers move on Earth?

 

[Pengwuino]

What makes a fan spin? If just put some fan blades on a pole in still air, do you think they'd move? Why do fans need electricity?

 

[amey_naik2812]

i agree that the fan won't move on the pole, but if u switch it on then wind will be generated...
wat do u say?

 

[Pengwuino]

Sure, if there is air around the fan, the fan will push the air around.

If you're in space where there is no air, the fan will spin, but there's no air to be pushed around.

 

[amey_naik2812]

@jack... its just a question with popped in my head...
but my intuition says it will move...
dnt know why..

 

[amey_naik2812]

@pengwuino
but my question is will the fan move or remain at the same position?

 

[Jack21222]

Things only move if there is a force acting on it. What force would be acting on the fan in space? What force acts on the fan on Earth?

 

[amey_naik2812]

wont the rotation of the blades of the fan create a force which might push the fan backwards...
Newtons law TO EVERY ACTION THERE IS AN EQUAL AND OPPOSITE REACTION...

 

[texasblitzem]

I'd like to chime in on this if no one minds. I think the fan blades will spin and the base will slowly start to spin in the same direction as the blades, just like a helicopter would if it did not have the tail rotor to counteract the rotation of the main rotor. But now I have a question, if the above is true.
Say the battery lasts forever, would the base start to catch up in speed to the fan blades? It seems the blades always have to go faster than the base, or else you'd end up with a spinning object in space. How fast would the base spin relative to the blades?
Or is my post nonsense? = )

 

[Jack21222]

The rotation of the blades would pull the center of the fan along in the direction of motion.

However, the blades go around in a circle, and we're assuming a symmetrical fan. For example, when the top blade is moving right, the bottom blade is moving left. When the right blade is moving down, the left blade is moving up. NONE of the blades is moving along the axis of rotation (which is what you mean by forward).

The forces associated with the fan blades moving cancel out.

Now, if you had an unbalanced fan, with, say, three blades on one side and none on the other, the fan would probably wobble around a little, but still wouldn't "go forward."

 

[Borek]

I think the fan blades will spin and the base will slowly start to spin in the same direction as the blades

Same or opposite?

 

[Pengwuino]

wont the rotation of the blades of the fan create a force which might push the fan backwards...
Newtons law TO EVERY ACTION THERE IS AN EQUAL AND OPPOSITE REACTION...

Yes but there is no air to push against so there's no force in the first place so the "equal and opposite" force wouldn't exist either.

However, as someone has pointed out, if the fan blades rotate, the rest of the fan will rotate as well, in the opposite direction to conserve angular momentum. So if you started up the fan in space, the fans would start going let's say, counter-clockwise, and the base of the fan would start turning clockwise. However there would be no movement of the system as a whole.

 

[amey_naik2812]

i would like to give an example...
take a torpedo and a missile into consideration, which are to move and hit a target underwater. Both work on the principle of action and reaction. Missile uses the force generated my compressed air while the torpedo has a fan at the back to push it forward...
correct me if i m wrong.
and if the spacecraft which burns the fuel to propel itself forward then why can't fan move or if the fan is attached to an object then won't the object move?
its just that the medium has changed for torpedo and missile the medium was water but for the spacecraft and the fan the medium is vacuum...
now the argument is that vacuum is nothing so there is nothing to push against and if that is the case then how come space ships move according to the principle of action and reaction??

 

[Jack21222]

i would like to give an example...
take a torpedo and a missile into consideration, which are to move and hit a target underwater. Both work on the principle of action and reaction. Missile uses the force generated my compressed air while the torpedo has a fan at the back to push it forward...
correct me if i m wrong.
and if the spacecraft which burns the fuel to propel itself forward then why can't fan move or if the fan is attached to an object then won't the object move?
its just that the medium has changed for torpedo and missile the medium was water but for the spacecraft and the fan the medium is vacuum...
now the argument is that vacuum is nothing so there is nothing to push against and if that is the case then how come space ships move according to the principle of action and reaction??

Rocket boosters in space don't work by pushing air out of the way. It works by "equal and opposite reaction."

Propellers (or fans) work by pushing air of the way. There is no air in space to push out of the way.

Surely you can see that rockets are actually firing particles out of the back end, while a fan in a vacuum fires out no particles.

 

[amey_naik2812]

jack please elaborate:)

 

[Jack21222]

jack please elaborate:)

Look at a rocket. You see particles flying out of the back. They propel the rocket forward even in a vacuum.

Look at a fan in a vacuum. There are no particles!

I don't see how I can make it any more clear.

 

[Pengwuino]

As Jack said, a missiles propulsion is coming from a controlled explosion. You have a chemical reaction that sends molecules flying away from each in opposite directions. Half the molecules in general fly out one end. The other end fly into the rocket, providing a push in a sense (don't quote me on that being exactly what it does but the basic idea is that the propulsion is due to reactions of chemicals already on the rocket). This is with no input coming from the atmosphere surrounding the rocket (except the oxidizer on a solid rocket i believe?). In fact, being in an atmosphere, if I recall, actually reduces the effectiveness of rockets a little, though again don't quote me on that.

A torpedo needs to push on something. It doesn't have its own supply of molecules to shoot out the opposite direction of where it wants to go. A rocket does.

Which makes me wonder if solid rockets work in space considering I believe they use oxygen in the atmosphere as an oxidizer.

EDIT: Ok so as I suspected, the solid rockets propellant has an oxidizer in it. Thus, the atmosphere a solid rocket is in is irrelevant, air or vacuum. Thank you Google.

 

[RichDIT]

Hello All,

A fan in a vacuum would behave as such...

When turned on, the motor inside the fan will receive energy from the battery, which in turn, will spin the propeller.

However, being a vacuum, there is no medium in which the propellers would be pushing against.

Propulsion from a propeller of, let's say, an aircraft, works by rotating through the air like a corkscrew or a screw through wood.

In space the propeller on our fan would spin but would have nothing to interact with.

The base of the fan would also be affected. For every force is an equal and opposite reaction.

If the motor is mounted to the base at a 90 degree angle, as most conventional fans, the amount of force that is needed to rotate the propellers in a clockwise direction is applied in the opposite direction where the motor is mounted.

The base would spin in the opposite direction as the blades.

Rocket propulsion works in a vacuum because the exploding force on the bottom of the rocket creates a force in the opposite direction. Keep in mind rocket fuel has a mixture of fuel and oxidizer (oxygen).

 

[amey_naik2812]

thank you everyone :)

 

[jared69sib]

What if you built a fan composed of 2 tubes (side by side length wise) with fans inside of each tube that spun in opposite directions? Would there be enough matter in space for the spinning blades to act upon creating a force? And if so would acceleration continue as the velocity increases?

 

[jared69sib]

Hmmmm...to modify my last post without deleting it let me try this again as an attempt to eliminate the vacuum issue...

*What if you built a fan composed of 2 funnels (side by side length wise) with fans inside of each funnel that spun in opposite directions? Would there be enough matter in space for the spinning blades to act upon creating a force? And if so would acceleration continue as the velocity increases?

****Or to really get things going what if we fed oxygen or some gas through this funnel? Or the tube?

 

[jared69sib]

The reason I even found this thread is because of my curiosity with 2 ideas...

The first being to discover a way to manipulate drag or resistance into becoming a force to help push the spacecraft along...I imagine we could reach the speed of light this way...

The second which is kind of similar would be to collect particles in space, and use them as a fuel source...obviously the faster the spacecraft travels the faster it would gather particles again creating an accelerating force.

**** If this idea is at all plausible, then this post stands as my copyright! LOL. Seriously! ****

 

[Rap]

A rocket shoots parts of its own mass backward, and the equal and opposite reaction is to move the rest of the rocket forward. A fan pushes mass that is nearby backwards, and so it goes forward. If there is no mass nearby, like air or water, then it cannot push anything backwards and so it goes forward.

If you have a fan spinning in empty space, it must conserve its original angular momentum, which was zero. Since the motor weighs more than the blades, it will turn more slowly than the fan blades, and in the opposite direction of the fan blades. If the fan blades are turning clockwise, the motor will turn more slowly in the counter-clockwise direction.

 

[jared69sib]

But what if you prevent the motor from spinning. Hence the reason I wanted to mount 2 tubes or funnels mounted adjacent to each other...


My only other argument is that there must be mass in space or else there would be no drag on a spaceship. How fast would the fan have to be traveling from the start to react with any space matter?

 

[JaredJames]

The second which is kind of similar would be to collect particles in space, and use them as a fuel source...obviously the faster the spacecraft travels the faster it would gather particles again creating an accelerating force.

There is already a hypothetical engine design which does this, a Bussard Ramjet: http://en.wikipedia.org/wiki/Bussard_ramjet

 

[russ_watters]

My only other argument is that there must be mass in space or else there would be no drag on a spaceship. How fast would the fan have to be traveling from the start to react with any space matter?

There is essentially no drag on spacecraft once they get a few hundred miles from Earth.

 

[Drakkith]

But what if you prevent the motor from spinning. Hence the reason I wanted to mount 2 tubes or funnels mounted adjacent to each other...


My only other argument is that there must be mass in space or else there would be no drag on a spaceship. How fast would the fan have to be traveling from the start to react with any space matter?

Space is a NEAR perfect vacuum. There are most definitely particles in space, however the density of the particles is extremely low. So low that once you get beyond the Earth's atmosphere it's pefectly acceptable to say that there is no drag for almost all purposes other than scientific experiments.

Using a fan as a propulsion method would never work, as even with a large funnel gathering the particles in front and compressing them at the fan would still result in far too small a quantity to perform any useful armount of work. Also, you cannot get to the speed of light Jared. Ever.

 

[JaredJames]

Also, you cannot get to the speed of light Jared. Ever.

I never said you could, I only pointed to the Bussard Ramjet.

EDIT: Oh, sorry. Just realized the other guys name.

 

[HallsofIvy]

What kind of "fan" are you talking about? If you are referring to a "pin wheel" that just has vanes attached to an axle, then because there is no air to push them, the vanes will not move.

If you are talking about an electric fan with, say, batteries in the handle, then the electric motor will cause the vanes to turn, whether there is air or not. If there is no air, then, of course, the fan will NOT cause a breeze since there is no air to move.

As far as "equal and opposite force" is concerned, if the fan, vanes together with the handle holding the batteries are not attached to anything, the vanes will turn in one direction, the handle in the opposite direction, at speeds so that energy is conserved (the total energy which is NOT direction dependent is the same as the electrical energy used) and so that the total angular momentum (which is direction dependent) is 0.

 

[jared69sib]

There is essentially no drag on spacecraft once they get a few hundred miles from Earth.

If that was true, the why would our ability to accelerate be limited? Surely, we could design a burst method to constantly accelerate no?

 

[jared69sib]

There is already a hypothetical engine design which does this, a Bussard Ramjet: http://en.wikipedia.org/wiki/Bussard_ramjet

Yea, I briefly read about this. I guess that is basically where my idea came from...the designs I had in mind though are quite different.

 

[JaredJames]

Jared, your last post is based on a severly flawed understanding of relativity.

This thread is not the place for that discussion.

 

[jared69sib]

Space is a NEAR perfect vacuum. There are most definitely particles in space, however the density of the particles is extremely low. So low that once you get beyond the Earth's atmosphere it's pefectly acceptable to say that there is no drag for almost all purposes other than scientific experiments.

Using a fan as a propulsion method would never work, as even with a large funnel gathering the particles in front and compressing them at the fan would still result in far too small a quantity to perform any useful armount of work. Also, you cannot get to the speed of light Jared. Ever.

We can't reach the speed of light YET! But it can be done. At least theoretically... The biggest concern would be having a medium that would not be destroyed at that velocity or putting in a system to provide temperature control, etc. The only thing stopping us from reaching the speed of light is G-Force, and a large enough fuel source. Wouldn't you agree?

 

[russ_watters]

If that was true, the why would our ability to accelerate be limited? Surely, we could design a burst method to constantly increase or acceleration no?

Our ability to accelerate is limited only by the fuel we can carry on our rockets.

We can't reach the speed of light YET! But it can be done. At least theoretically... The biggest concern would be having a medium that would not be destroyed at that velocity or putting in a system to provide temperature control, etc. The only thing stopping us from reaching the speed of light is G-Force, and a large enough fuel source. Wouldn't you agree?

No, reaching light speed is forbidden by scientific theory.

 

[Drakkith]

We can't reach the speed of light YET! But it can be done. At least theoretically... The biggest concern would be having a medium that would not be destroyed at that velocity or putting in a system to provide temperature control, etc. The only thing stopping us from reaching the speed of light is G-Force, and a large enough fuel source. Wouldn't you agree?

Nope. As your velocity increases, it takes more and more energy to accelerate. It takes an infinite amount of energy to make something with mass reach the speed of light. It cannot be done, not even theoretically.

 

[jared69sib]

Our ability to accelerate is limited only by the fuel we can carry on our rockets. No, reaching light speed is forbidden by scientific theory.

Please excuse my ignorance, but why is it forbidden? I am sure it is based on a equation, but just have to ask.

 

[jared69sib]

Nope. As your velocity increases, it takes more and more energy to accelerate. It takes an infinite amount of energy to make something with mass reach the speed of light. It cannot be done, not even theoretically.

But let's imagine an unlimited fuel source for a moment...

Maybe we could send some unmanned spacecraft ahead with extra fuel, since G-Force is not a factor...

Or maybe we can abandon rocket fuel as a source once we exit the atmosphere, and use something lighter like compressed hydrogen some how... (I'm still thinking about that fan, but so reluctant to say it).


Or beam lasers at the space craft...

 

[russ_watters]

Please excuse my ignorance, but why is it forbidden? I am sure it is based on a equation, but just have to ask.

Einstein's theory of Special Relativity states that to any observer, the speed of light is always the same. In other words, no matter how fast you think you're going or how long you're accelerating, you'll always be zero with respect to the speed of light. So even when chasing a beam of light, it'll always move away from you at the speed of light.

In a rocket, it means that to an outside observer your acceleration will continuously decrease and you'll get closer and closer to the speed of light without ever reaching it while to you, in your spacecraft , you'll always feel the same acceleration.

http://en.wikipedia.org/wiki/Special_relativity

 

[JaredJames]

An unlimited source of fuel doesn't exist. There is no such thing as "infinite energy". It is this that makes attaining light speed impossible.

 

[jared69sib]

Nope. As your velocity increases, it takes more and more energy to accelerate. It takes an infinite amount of energy to make something with mass reach the speed of light. It cannot be done, not even theoretically.

To me it seems that the amount of energy required cannot be infinite. A simple law in calculus tells you that anything finite or that can be defined must contain all finite parts... Not the exact wording, but you get the gist...

If something like the speed of light can be defined as 186,000 miles/sec, then it is a finite number correct? It is not an infinite speed... Unless however that little bit of drag that doesn't make a difference now does in this situation... (I think it does)... So the acknowledgment of drag is important... so even the light must succumb to drag...otherwise there wouldn't be any limit... and light is the fastest thing we know of correct?

I think drag should be considered for us to conquer this problem.

What do you guys think of graphene? Electricity can travel at 200,000 cm2 V−1s−1 and 40,000 cm2 V−1s−1 based on some limiting factors. I'm guessing s stands for seconds right? It's conductivity slows down quickly, but I remember hearing something about it approaching light speed...******Light speed is 186,000 miles/sec, not hour. I changed it above. TYPO! Brain glitch! LOL.

 

[jared69sib]

Einstein's theory of Special Relativity states that to any observer, the speed of light is always the same. In other words, no matter how fast you think you're going or how long you're accelerating, you'll always be zero with respect to the speed of light. So even when chasing a beam of light, it'll always move away from you at the speed of light.

In a rocket, it means that to an outside observer your acceleration will continuously decrease and you'll get closer and closer to the speed of light without ever reaching it while to you, in your spacecraft , you'll always feel the same acceleration.

http://en.wikipedia.org/wiki/Special_relativity

I think we just can't go fast enough yet...

 

[jared69sib]

An unlimited source of fuel doesn't exist. There is no such thing as "infinite energy". It is this that makes attaining light speed impossible.

So that supports my theory that the fuel source to achieve light speed is finite.

Thanks for humoring me everybody. LOL. I still have a lot to learn, but there are all some of the very basic and primitive ideas shooting around my noggin. Einstein was a bad-*** rebel in his day right? We need a new rebel! :)

 

[russ_watters]

I think we just can't go fast enough yet...

Well, you're wrong, plain and simple. And your speculations above are wrong too (essentially everything in your previous post was wrong, including the speed of light). There is a lot that you don't know about how the universe works, but just because you don't know, that doesn't mean others don't know and it doesn't make your speculations reasonable, it makes them foolish. More to the point, this forum is for learning real science, not for idle speculation. Please keep that in mind.

 

[cdotter]

To me it seems that the amount of energy required cannot be infinite. A simple law in calculus tells you that anything finite or that can be defined must contain all finite parts... Not the exact wording, but you get the gist...

Math is a human construct and nature is not.

 

[JaredJames]

So that supports my theory that the fuel source to achieve light speed is finite.

No, it says the exact opposite.

Thanks for humoring me everybody. LOL. I still have a lot to learn, but there are all some of the very basic and primitive ideas shooting around my noggin. Einstein was a bad-*** rebel in his day right? We need a new rebel! :)

With your current knowledge and understanding, it certainly won't be you.

 

[jared69sib]

Well, you're wrong, plain and simple. And your speculations above are wrong too (essentially everything in your previous post was wrong, including the speed of light). There is a lot that you don't know about how the universe works, but just because you don't know, that doesn't mean others don't know and it doesn't make your speculations reasonable, it makes them foolish. More to the point, this forum is for learning real science, not for idle speculation. Please keep that in mind.

Well, I am trying to learn. You don't need to be so blunt. And I fixed my little typo above about the speed of light...fyi.

 

[jared69sib]

No, it says the exact opposite.


With your current knowledge and understanding, it certainly won't be you.

Your comment was also not necessary.

 

[jared69sib]

If your goal doesn't include motivating a young or new enthusiast, then what are you doing on this forum. I certainly wouldn't appreciate you talking to my son that way...

 

[JaredJames]

You are claiming that published science is wrong. Read the materials and learn from it. I assure you, all the stuff you're thinking about it has already gone through someones mind.

Next time, ask why something is what it is and don't simply tell us it is wrong. Then you'll avoid such reactions.

And no, my goal isn't to motivate. It is to help educate others and learn more myself.

Anyone who wants to be overly speculative and make ridiculous claims doesn't belong here. Those are the rules.