Earth spins at 450mph

digme

If I had a balloon and left it float up into the air without being attacked to a string back down to the ground, and there was zero wind speed that day;why does the balloon stay in the same place?Is it because the balloon is also going 450mph?

Michael Collins

Yes, because the air is also going at the speed of the earth.

jhegarty

Short answer, gravity.

Michael Collins

And just to add to my previous post, the ballon was going at the speed of the earth when it was on the earth & it will continue to do so unless some force acts on it in such a way to change that speed.

geminidawn

It would never happen, even if the earths atmosphere was dead calm the rotation of the earth alone would cause an apparent wind where due to turbulence the air closest to the earth would move faster than the air higher in the stratosphere, as your balloon would rise it would appear to drift east when in fact as it rises it would escape the stronger turbulence and get left behind.

Turtwig

My favourite answer to this question is giving in the recent debunking of the movie Star Trek.

Intuitor wrote:

The edge of outer space is considered to be about 73 miles (118 km) above the surface of Earth. To orbit at this height, a spacecraft would need to be traveling at a speed of 17,500 mph (28,200 kph). Under these conditions, an orbiting spacecraft could not possibly hover over a fixed point. It would be traveling over 27,000 mph (43,500 kph) relative to the ground! In order to hover, a spacecraft would need to slow down to zero speed relative to the ground and then expend enormous amounts of energy by blasting large amounts mass out its downward thrusters in order to counteract gravity.

This shows how hard it is for a spaceship with a drill drilling the same spot in the earth to stay in one fixed location relative to the ground, hopefully you can see that as your balloon rises it's situation would become closer and closer to that of the spaceship..i.e it is practically impossible for it to stay in the same place relative to the ground.

I don't consider the above post a spoiler but if the mods or anyone think it is feel free to edit it or PM me.

Capt'n Midnight

Malty_T wrote: »

My favourite answer to this question is giving in the recent debunking of the movie Star Trek.

This shows how hard it is for a spaceship with a drill drilling the same spot in the earth to stay in one fixed location relative to the ground, hopefully you can see that as your balloon rises it's situation would become closer and closer to that of the spaceship..i.e it is practically impossible for it to stay in the same place relative to the ground.

The craft in questionhas warp drive, it can go faster than light
not sure what the impulse engines can do but even if they can only go to 0.5 c that is way more than is needed to hover above a fixed point

in Star trek physics there are tractor beams, it could use a tripod of these perhaps

they had the technology to drill to the core of a planet

Mr Clarke said something about advanced technology looking like magic didn't he ?




If you lift a balloon above a non rotating planet it will fall to the planet ( assuming no other bodies to attract it)
If the planet rotates then the balloon will rotate with it. If you hold the balloon at twice the radius of the planet it will be rotating at 900mph above a stationary point. If you hold it high enough it will rotate fast enough to stay in orbit (remember higher orbits are slower since further up the gravity well or away from the gnomes depending on which model of gravity you use)

the air analagy is the same as when you are in an aeroplane jump up and down and you move at the same speed as it

http://www.astronautix.com/craft/echo.htm - balloons in orbit 30 m in diameter but the orbital period was 117 mins ( to cover over 40,000 Km )


oh BTW you weigh less at the equator than at the poles

Delphi91

Malty_T wrote: »

...This shows how hard it is for a spaceship with a drill drilling the same spot in the earth to stay in one fixed location relative to the ground, hopefully you can see that as your balloon rises it's situation would become closer and closer to that of the spaceship..i.e it is practically impossible for it to stay in the same place relative to the ground...

That's why Star Trek is an example of science FICTION

bildo

It's all relative my friend. Similar to the example given by Einstein in his books of a man walking towards the from of a train carriage. To an observer standing by the tracks he appears to be moving at a the speed of the train plus the speed at which me walks where to a onlooker inside the carriage simply sees a man walkin normally.
What speed is the man travelling? There are simply 2 answers depending on your viewpoint, both equally valid. This is the essence of relativity. I urge you to get a book on it and think for a while.

Look at the balloon's movement relative to the earth, the observer and to a satellite in space both in relation to the earths surface and the center of the earth. Each perspective will give you a completely different measurement of movement. Again, each is correct to the onlooker in his relation to the balloon.

Kevster

Look, just go down to the pound shop, buy the friggin' balloons, and do the experiment :P

I liked the example that Malty gave, but more-so geminidawn's example - I think that explains it the best. Gravity is also a consideration, obvioudsly, but wind would have the most profound efect on the position of the balloon.

Capt'n Midnight

Just to mention the 450mph depends on where you are

you weigh less at the equator than at the pole because of the centrifugal force
that and the sweating and extra clothes


seriously you have to remember Newton's laws of motion , the one where things keep moving unless there is outside inteference

Bodicea

If memory serves there was something like this in the science museum some 10-15 years ago. It might be still there, not sure.

but they had built some sort of platform that was independant and not subject to the rotation of the earth. (I know, sounds impossible but cant remember how they did it). Any way, it proved that if something was detached from earth then the earth would rotate under it and the object wouldnt be affected by it.

Badly written and explained I know, but it was a very long time ago.

Basically, the atmosphere is attached to the earth and rotates with it. If a balloon is let off and not attached to the earth then it will be affected only by the winds. It think it was the Japanese that used this to their benefit. They sent balloons into the jet stream. The balloons were carried to the US (think there were bombs in the balloons).

It might be a dead still day where you are standing, but there are still upper atmosphere winds on the go, born in the doldrums.. Otherwise our weather systems would come to a standstill.

Bodicea

Meant to add, that yes, if it were a dead still day, no winds and the balloon stayed at the same level, but yet not high enough to be affected by the upper atmosphere winds, jets stream etc, then yes, it will travel at the same speed as the earth, simply becuase it is so light and would be at the mercy of the atmosphere and carried along with it, cos the atmosphere is travelling along with the earth.

If it were a much heavier object, say a helicopter, or something that wouldnt be so easily carried, then it would stay static, and as the earth revolved it would leave the helicopter behind, only to reappear from the east in 24 hours.

sebastianlieken

gravity?.... RELATIVITY?... I take it that some of you guys like the sounds of your own voices!?

It's because we live within the momentum boundary layer of the earth (the atmosphere). we can consider one of the boundary conditions to be a "no-slip" condition. Which means: the airspeed directly at the surface of the earth is 0m/s. the higher and higher you go, the faster the air will move relative to the earths surface. (you gotta go very high for this, i.e space....)

Sheeps

if theres a plane on a threadmill and the threadmill is rotating at the speed required to take off for the aircraft the plane will take off

Bodicea

sebastianlieken wrote: »

Which means: the airspeed directly at the surface of the earth is 0m/s.

Eh?

Kevster

Sheeps wrote: »

if theres a plane on a threadmill and the threadmill is rotating at the speed required to take off for the aircraft the plane will take off

No chance. There's no change in air-pressure in this scenario, which is what the airplane needs. An airplane obtains 'lift' by air moving faster over it's wing than under it. This creates a higher pressure under the wing, which then generates lift.

Air moves from high to low pressure.

Kevin

Turtwig

Kevster wrote: »

No chance. There's no change in air-pressure in this scenario, which is what the airplane needs. An airplane obtains 'lift' by air moving faster over it's wing than under it. This creates a higher pressure under the wing, which then generates lift.

Air moves from high to low pressure.

Kevin

?

Experiment proves otherwise.

Perhaps you need to re-evaluate your model.

thecornflake

it looks like he is moving forward on that "conveyor belt" , so could still cause a difference in air pressure. I dont know what they were trying to do there but even the commentator said the both car and plane were accelerating away from each other.

Podge_irl

Sheeps wrote: »

if theres a plane on a threadmill and the threadmill is rotating at the speed required to take off for the aircraft the plane will take off

No chance. There's no change in air-pressure in this scenario, which is what the airplane needs. An airplane obtains 'lift' by air moving faster over it's wing than under it. This creates a higher pressure under the wing, which then generates lift.

Air moves from high to low pressure.

Kevin

The initial set-up is very poorly worded making it difficult to know exactly what scenario we're dealing with here.

There needs to be airflow over the wings for a plane to take-off, that's all that matters. A plane will take off if this air-flow is quick enough. The plane takes off in the treadmill experiment done on Mythbusters because the thrust for a plane doesn't come through the wheels and so being on a treadmill makes no real different to the plane.

Sheeps

Podge_irl wrote: »

The initial set-up is very poorly worded making it difficult to know exactly what scenario we're dealing with here.

Yes, that was the point. It was an ironic post. Jesus stop debating this.

Sheeps

gah...

Professor_Fink

sebastianlieken wrote: »

It's because we live within the momentum boundary layer of the earth (the atmosphere). we can consider one of the boundary conditions to be a "no-slip" condition. Which means: the airspeed directly at the surface of the earth is 0m/s. the higher and higher you go, the faster the air will move relative to the earths surface. (you gotta go very high for this, i.e space....)

Actually that's not at all true. If the earth was spun faster and faster, so that the rate of rotation was increasing you would still have zero airspeed at the interface of the ground and the air. However, the rest of the atmosphere would not be keeping pace, and you'd be generating vortices.

The reason the air keeps pace with the earth is essentially a mixture of the two explanations. The relative motion is all that matters since the atmosphere is thin relative to the radius of the planet.

Kevster

Malty_T wrote: »

?

... ...

Experiment proves otherwise.

Perhaps you need to re-evaluate your model.

Christ man, you could have phrased your original post better don't you think? You didn't leave me with any option but to cast aside what you originally said. Be more thoughtful in future (and not try to be sensationalistic), will you?

Kevin

Added: Just realised it wasn't you who made the comment originally! :P