Theoretical question

[Munchkin71]

Pure fantasy here, but please bear with me!

Assuming it were possible to levitate (I know, big 'if'!), and you started levitating from a standing position on a train moving at a constant speed, would you stay fixed at the same point, or would the train 'catch you up' until you hit the back of the carriage?

This poser has divided my friends, half believe the lack of outside influence would maintain your position, the other half expect to meet the back of the train fairly rapidly! Any thoughts please?

[gastwo]

Lack of outside influence would maintain your position.

Try throwing somthing up in the air in a carriage/car/plane - it comes back down to you.

[jake-the-peg]

If you started to levitate when the train was moving you would also be moving at that speed.

It would take an external force to slow you. Given that the air in the train is travelling at the same speed, drag from wind resistance would not do that, so you would keep up with the train.

If you tried the same trick on an open flat bed carriage wind resistance would rapidly slow you.

[Munchkin71]

Thanks guys, that was quick - and very interesting.

As an aside however, one of the counter-arguments went like this... Supposing you were hanging unobstructed from the roof of the carriage by a rope (closest to levitation we could manage), would you expect to be hanging straight down perfectly vertical, or at a slight angle backwards, against the motion of the train? I find both hard to imagine.

[ugly_bob]

straight down. unless the train changed speed. same with the levitation. If the train accelerated, you'd hit the back of the carriage, if it braked, you'd hit the front.

[Tim123]

Motion doesn't require a force. A change in motion (acceleration) does. As long as the train is not accelerating, no forces other than gravity will be acting on you so you will hang vertically.

If you tried the same thing in your house, which is moving at hundreds of miles an hour due to the rotation of the earth, you would hang vertically also.

[jake-the-peg]

You'd hang straight down.

You need to grasp the difference between moving at a constant speed and accelerating.

You are sitting reading this at the moment yet you are wizzing through the universe at thousands of miles a second relative to other stars and planets about you.

Thing is you can't tell that because the speed is constant. You only get forces when you accelerate - being pressed back in your seat when a plane takes off but not when you're cruising along at 30,000 feet or whatever it is.

Imagine a bullet fired from a gun that breaks up in flight - all the pieces are still doing the same speed - it's like if you jump up and down in a plane you may not be attached to the plane but you're still travelling at hundreds of miles an hour

[Loosehead]

It's all about relativity, essentially the path you appear to take depends on the viewpoint. From inside the train you go up and down on the same spot (forget levitation, just jump up). Viewed from outside the train you would appear to trace and arc through the sky. This question is a regular here in different forms.

See here for example

http://www.theanswerbank.co.uk/Science/Question227433.html

[Munchkin71]

Thanks again everybody - very illuminating!

[mibn2cweus]

�Any thoughts please?� Music to my ears! As you wish:

In a sense, the man standing in the train, the train itself, the tracks the trains wheels are rolling on, the railroad ties and the Earth supporting them are all levitating, (in as much a levitation makes any sense), otherwise, the man, the train, you and me and the Earth itself would all accelerate downward into the center of gravity created by the Earth�s mass. It is this constant downward acceleration of gravity countered by the repulsive force of the electrons surrounding the atoms of which everything is made that keeps us all in a place we would soon appreciate immensely if gravity were suddenly and mysteriously turned off. If this were to suddenly happen to the man standing in the train the recoil of his body mass, from the disappearance of the one hundred or so kilograms provided by gravity, would hurl him violently into the ceiling of the train car in which he had been riding.

continued . . .

[mibn2cweus]

Part of an astronauts training involves exposure to �zero gravity� for the purpose of becoming familiar with the experience and seeing if this causes them unacceptable discomfort. A plane takes them up high in the sky and is then guided into a decelerated rate of ascent followed by a freefall and accelerated decent all the while compensating only for the aerodynamic influences of the plane flying through the air. During this �zero gravity� portion of the flight they levitate freely within the plane although it is constantly altering its vertical speed and direction of flight to precisely compensate for the downward acceleration of the Earth�s gravity.

So in effect, we are all not only moving but also constantly accelerating where we stand!

[Xollob]

Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.
The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.

From The Meaning of Life. Does this answer your question?

[lord molly]

when i was little, i used to be afraid jump on a plane, thinking i would be splattered agains a hostess or the back.

but like every one else is saying, it is a poo idea that it would happen, as the capsuel and everything inside it is movig with the train, so would you

[woodchopper]

So how does Paul Daniels make someone levitate and then pass a solid metal ring over them to disprove the supposition of being suspended by wires ??

[Munchkin71]

I could answer that one, but then the Magic Circle would have to kill you...

If you really, really want to know read "Hiding the Elephant" by Jim Steinmeyer (ain't I a tease?).