Sciencemadness Discussion Board - Why wont it fly?

Why wont it fly?

D4RR3N - 18-12-2013 at 15:02

I found this image whilst looking for inertial propulsion devices. Whilst I don't believe it will lift off under its own power I'm not sure at the same time why it should not.

Lets say the device is pumping a liquid with a large mass such as mercury at high velocity over the arced section. If we put arrows on the diagram showing the centrifugal force of the mercury being flung against the wall of the arc like clothes in a spin dryer none of the arrows point down. All the arrows point either horizontal or in an upwards direction. This would lead you to imagine this thing must lift off the table but it cant be. So my question is please explain to me why it wont go airborne

DubaiAmateurRocketry - 18-12-2013 at 15:04

It obviously wont fly, just like putting a huge magnet infront of your car, but is also hanged from your car. The force is in the same system. Do you fly when you push your self ?

bfesser - 18-12-2013 at 15:05

When you draw in vectors for all of the forces involved, you should immediately see why it won't fly.

This sort of thing is popular on 4chan.org/b/:

Troll+physics_0b2b4c_4210419.png - 200kB

[Edited on 18.12.13 by bfesser]

D4RR3N - 18-12-2013 at 15:16

http://www.youtube.com/watch?v=QI-7wA8lYGU

OK if you say an object can not be moved in its self explain why the above toy is moving. My dog has the same toy and all it consists of is an eccentric spinning weight inside the ball ie it is being moved by the centrifugal force of a spinning mass from within the ball.

[Edited on 18-12-2013 by D4RR3N]

bfesser - 18-12-2013 at 15:21

Quote: Originally posted by bfesser

draw in vectors for all of the forces involved

D4RR3N - 18-12-2013 at 15:25

Quote: Originally posted by bfesser

draw in vectors for all of the forces involved

Ok the liquid is rising up one side and descending down the other so those two cancel out...then we are just left with the centrifugal force and all those arrows point either horizontal or up.

bfesser - 18-12-2013 at 15:29

What about the forces exerted by the pipe on the liquid which diverts it's horizontal flow at right angles? What about the inertia of the liquid? And let's not forget gravity!

[edit] Perhaps this image will help you to understand, if you can draw in the force vectors here to show why it's silly. It's very similar to what you're asking.

[Edited on 18.12.13 by bfesser]

D4RR3N - 18-12-2013 at 15:40

Quote: Originally posted by bfesser

What about the forces exerted by the pipe on the liquid which diverts it's horizontal flow at right angles? What about the inertia of the liquid? And let's not forget gravity!

Obviously gravity pulls down!

the momentum of the fluid in the horizontal pipe is horizontal and not downwards.

Care to explain why the toy moves if a spinning mass cannot produce thrust?

It is not at all similar to the images you posted...and again why does the toy move?

[Edited on 18-12-2013 by D4RR3N]

Marvin - 18-12-2013 at 15:52

An eccentric spinning weight will just spin around it's center of mass if not touching anything else but as soon as it contacts a surface it has leverage.

To make the problem simpler try ignoring gravity and list the forces as they affect 1 molecule of liquid going round the loop.

D4RR3N - 18-12-2013 at 16:03

Where in the system (other then the forces I already mentioned) points down to equal the upward force?

D4RR3N - 18-12-2013 at 16:06

Quote: Originally posted by Marvin

An eccentric spinning weight will just spin around it's center of mass if not touching anything else but as soon as it contacts a surface it has leverage.

To make the problem simpler try ignoring gravity and list the forces as they affect 1 molecule of liquid going round the loop.

True but if you hold that toy in your hand it shakes your hand as you would expect so the argument of a person lifting themselves up by their own shoe laces don't cut it.

[Edited on 19-12-2013 by D4RR3N]

Marvin - 18-12-2013 at 16:29

Just considering the vertical components, as a molecule moves round it is accelerated up by the container, producing a downwards force on it, moved round in a circle ( producing an upwards force on the container ) and then decelerated to move along the straight. The molecules are moving up at one end and are moving down at the other, so you might think those forces cancel out.

Accelerating a ball toward the sky requires an upwards force. Decelerating a falling ball *also* requires an upwards force.

The arc of the container is being forced upwards by the liquid, but it being pushed down by *both* ends.

cyanureeves - 18-12-2013 at 16:48

so if dropped from an apple tree it would spin like that toy before it hit the ground then take off in the direction of the arrows?aint no telling what it would do in space.

D4RR3N - 18-12-2013 at 16:48

The pump is in the center of the horizontal pipe so it will suck and push with equal force on both ends of the arc, this would mean the fluid ascends upwards and descends downwards with equal force, these two forces are equal in magnitude and opposite in direction so they must cancel to produce zero net momentum.

I still don't see the downward force to balance the largely upward centrifugal force, if I could see it I would not be asking the question!

gregxy - 18-12-2013 at 17:40

centrifugal force is proportional to mv^2/r

The radius of curvature for the two lower corners is smaller so they produce a larger force than the upper curved surface. V is about the same through the pipe. So the downward force from the lower 2 corners cancels the force from the upper surface.

Or from the the laws of economics: If the thing did work people would be using it all over the place and airplanes would not need any of those silly wings. So why do airplanes have wings?

IrC - 18-12-2013 at 20:13

Why wont it fly?

Because it couldn't reverse engineer Owsley's formula for grey.

Newton cannot answer either since he is busy spinning in his grave.

D4RR3N - 19-12-2013 at 01:33

Quote: Originally posted by gregxy

centrifugal force is proportional to mv^2/r

The radius of curvature for the two lower corners is smaller so they produce a larger force than the upper curved surface. V is about the same through the pipe. So the downward force from the lower 2 corners cancels the force from the upper surface.

Or from the the laws of economics: If the thing did work people would be using it all over the place and airplanes would not need any of those silly wings. So why do airplanes have wings?

OK the first serious attempt to explain the opposing force, thanks good answer!

If the centrifugal force generated by the fluid making a tighter turn at the two corners was greater then that over the larger arc would it not then press into the Earth?

They must be equal not greater to cancel forces out, otherwise I simply need to flip it then it will fly lol

[Edited on 19-12-2013 by D4RR3N]

Marvin - 19-12-2013 at 05:24

Quote: Originally posted by D4RR3N

The pump is in the center of the horizontal pipe so it will suck and push with equal force on both ends of the arc

You don't need a pump. If you assume no friction the liquid will continue to flow anyway, if you add a pump it applies no force except to overcome friction.

Quote: Originally posted by D4RR3N

this would mean the fluid ascends upwards and descends downwards with equal force, these two forces are equal in magnitude and opposite in direction so they must cancel

Ascending and descending are velocities, no forces are involved. Acceleration requires force, as is needed for something to change direction.

The acceleration is in the same direction at both ends, so the force is in the same direction. The same magnitude in the same direction, they do not cancel, they add.

When gregxy says centrifugal force, what he means is centripetal force. Centrifugal force does not appear because it does not exist. Objects travel in a straight line with constant velocity unless acted on by a force (first law). The centripetal force applied to a swinging bucket on a string for example, the force that keeps the string taut, is balanced by the need to accelerate the bucket to stay in an arc. Why is this important? You don't get an extra force from considering the acceleration of the liquid, it's just a convenient way of calculating it in a circle.

Yeah, I sound like a pedant, but if you don't setup the forces properly you only get the right answer by accident.

Paddywhacker - 20-12-2013 at 02:48

It cannot fly because it is missing something. An apostrophe.

> Yeah, I sound like a pedant, ...

Me too