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.