Counteracting the inertia of Earth's rotation

[Vic43]

TL;DR Summary

Hi guys , I'm a layman looking for an expert answer on the following hypothetical situation.

I am at the equator with a drone capable of 1000mph speeds and the ability to hover. If the sun (or another fixed point in space) was directly overhead and I waited for the earth to rotate 1000 miles then launched the drone and flew 1000mph against the earths spin till the sun was directly overhead again then hovered at that point, the earth should then be spinning under the drone right?
Much the same as if I were standing on a conveyor belt I would move with it , but if I ran against it at the same speed I would be running on the spot while the belt moves under me.

 

[Baluncore]

Welcome to PF.

All things are relative. You must move with the surface of the Earth, or it will slap you with a mountain, or drown you.
What are you trying to solve?
What precisely is your question?

 

[Vic43]

Welcome to PF.

All things are relative. You must move with the surface of the Earth, or it will slap you with a mountain, or drown you.
What are you trying to solve?
What precisely is your question?

Will the earth spin under the hovering drone in the above scenario? Considering in the scenario the hovering point is a point n space and not on earth.

 

[Baluncore]

Considering in the scenario the hovering point is a point n space and not on earth.

The drone is hovering in the atmosphere, and that is part of the surface of the Earth, in the same way that the oceans are part of the surface of the Earth. Do fish swim in space, or in the surface of the Earth?

 

[Vic43]

The drone is hovering in the atmosphere, and that is part of the surface of the Earth, in the same way that the oceans are part of the surface of the Earth. Do fish swim in space, or in the surface of the Earth?

That isn't a good analogy. The atmosphere isn't part of the earths surface.

 

[Vic43]

That isn't a good analogy. The atmosphere isn't part of the earths surface.

Think about a long conveyer belt , there is a mid point marker. Sit the drone on the conveyor belt at the marker , start the conveyor belt, let the drone move on the belt for a distance so it's moving at the same speed as the belt, then take off , fly it back to the marker and hover , the belt will move under the drone while it hovers at the marker. You've countered the inertia that was imparted onto the drone from the belt.

 

[Baluncore]

The atmosphere isn't part of the earths surface.

Many birds fly in the atmosphere, and nest in the same tree every night.

 

[Vic43]

Many birds fly in the atmosphere, and nest in the same tree every night.

Are you trolling ?

 

[Vic43]

Many birds fly in the atmosphere, and nest in the same tree every night.

Think about a long conveyer belt , there is a mid point marker. Sit the drone on the conveyor belt at the marker , start the conveyor belt, let the drone move on the belt for a distance so it's moving at the same speed as the belt, then take off , fly it back to the marker and hover , the belt will move under the drone while it hovers at the marker. You've countered the inertia that was imparted onto the drone from the belt.

 

[Drakkith]

If the sun (or another fixed point in space) was directly overhead and I waited for the earth to rotate 1000 miles then launched the drone and flew 1000mph against the earths spin till the sun was directly overhead again then hovered at that point, the earth should then be spinning under the drone right?

Yes, essentially. If you're wanting to cancel out Earth's rotation precisely you'd need to use the background stars as your reference target, or some ultra-precise gyroscope or something, as using the Sun will introduce a small error since we are moving around the Sun at the same time that we are rotating and have to rotate a bit more than 360 degrees to get the Sun back in the same spot in the sky a day later.

 

[PeroK]

Think about a long conveyer belt , there is a mid point marker. Sit the drone on the conveyor belt at the marker , start the conveyor belt, let the drone move on the belt for a distance so it's moving at the same speed as the belt, then take off , fly it back to the marker and hover , the belt will move under the drone while it hovers at the marker. You've countered the inertia that was imparted onto the drone from the belt.

If you want to avoid spinning with the Earth's surface and atmosphere, you'll have to fly with a ground speed of about $1600 \ km/h$ west (at the equator).

 

[Bandersnatch]

That isn't a good analogy. The atmosphere isn't part of the earths surface.

If you ignore the atmosphere (e.g. it's an airless planet and the drone uses rockets for propulsion), then you can hover the drone in one spot w/r to the background stars (or the Sun) after decelerating from the initial velocity imparted by the rotational motion of the planet while the planet itself rotates under it.
The point Baluncore was making is that if you don't ignore the atmosphere, then the drone needs to keep moving to stay in one spot, as the atmosphere is dragged by the surface. I.e. the medium used for propulsion by the drone moves at ~1000mph w/r to the background stars and if the drone stops flying against it, it'll be dragged with it to match the surface rotation too.

 

[Vic43]

If you want to avoid spinning with the Earth's surface and atmosphere, you'll have to fly with a ground speed of about $1600 \ km/h$ west (at

If you ignore the atmosphere (e.g. it's an airless planet and the drone uses rockets for propulsion), then you can hover the drone in one spot w/r to the background stars (or the Sun) after decelerating from the initial velocity imparted by the rotational motion of the planet while the planet itself rotates under it.
The point Baluncore was making is that if you don't ignore the atmosphere, then the drone needs to keep moving to stay in one spot, as the atmosphere is dragged by the surface. I.e. the medium used for propulsion by the drone moves at ~1000mph w/r to the background stars and if the drone stops flying against it, it'll be dragged with it to match the surface rotation too.

Thanks, I am sceptical about your last sentence though. There may be zero wind at the point you are hovering right? What will cause the drag on the drone if not the air itself in the form of wind? Actually the wind could be going the opposite direction.

 

[PeroK]

Thanks, I am sceptical about your last sentence though. There may be zero wind at the point you are hovering right?

No. The drone would need to fly at supersonic speed. Otherwise, you could fly in a helicopter from London to New York in 3 hours simply by hovering. You can only get from London to New York by flying at $1000 \ km/h$ through the atmosphere for about 5 hours. You can't do it by hovering in the atmosphere.

 

[Vic43]

No. The drone would need to fly at supersonic speed. Otherwise, you could fly in a helicopter from London to New York in 3 hours simply by hovering. You can only get from London to New York by flying at $1000 \ km/h$ through the atmosphere for about 5 hours. You can't do it by hovering in the atmosphere.

Sorry was replying to a different comment by bandersnatch

 

[Vic43]

I find this super interesting , I wonder if any experiments have been done?

 

[PeroK]

I find this super interesting , I wonder if any experiments have been done?

You mean like a worldwide commercial airline network?

 

[Bandersnatch]

Thanks, I am sceptical about your last sentence though. There may be zero wind at the point you are hovering right? What will cause the drag on the drone if not the air itself in the form of wind? Actually the wind could be going the opposite direction.

The air is rotating with the planet. Wind is motion of the air w/r to the observer (here, the drone). Since you've chosen the spot for hovering to be somewhere around the equator, as that's where the rotation velocity at the surface is approx. 1000mph, it would mean the still air is moving at that velocity w/r to the drone and the still air is perceived as 1000mph wind. Now, you could have some non-still air where the drone hovers, i.e. some local winds, that would change the perceived wind speed in either direction. But since there are no 1000mph winds even in the strongest hurricanes, you could never expect to nullify all that wind coming from the rotation of the atmosphere.
Of course you could have instead chosen a spot somewhere near the poles, where the rotation can be as leisurely as you want, including no rotation at all (at the poles). One can easily imagine some local wind patterns at least momentarily exactly matching the rotational velocity of the atmosphere so that your drone can hover in a spot.

 

[sophiecentaur]

Thanks, I am sceptical about your last sentence though. There may be zero wind at the point you are hovering right? What will cause the drag on the drone if not the air itself in the form of wind? Actually the wind could be going the opposite direction.

Do the experiment with just a balloon; a hovering drone adds pointless complication. It's a windless day. The air and the ground and the balloon (only just managing to float) are all stationary relative to each other. You let the ball gently float upwards.
IS there any force on the balloon that would make it move east / west or will it just hang there?
You try the same experiment on the roof of a train. What happens to the balloon and why?

 

[Vic43]

You mean like a worldwide commercial airline network?

No because they can't hover , but yeah I guess they should be gaining speed relative to the ground (or the ground should be moving opposite to the plane) if they flew long enough in a straight line along the equator. Maybe they have to accelerate less after a certain distance to maintain the same speed relative to the ground.

 

[Vic43]

Do the experiment with just a balloon; a hovering drone adds pointless complication. It's a windless day. The air and the ground and the balloon (only just managing to float) are all stationary relative to each other. You let the ball gently float upwards.
IS there any force on the balloon that would make it move east / west or will it just hang there?
You try the same experiment on the roof of a train. What happens to the balloon and why?

I get what you are trying to say, but I disagree. The drone doesn't complicate it, and is a better tool as it has propulsion. The balloon will be moved by the wind in the Train example , if you let the balloon go when you are stationary the wind could be going any direction at the time and I don't think any force will be imposed on it if there is absolutely zero wind in the area. Similarly with the drone example , once it flew far enough against earths spin to counter the inertia the place where it hovered could have any wind direction at the time, just because it was flying against the direction of the spin doesn't mean it somehow affects the local wind at the destination of hover.

 

[Vic43]

The air is rotating with the planet. Wind is motion of the air w/r to the observer (here, the drone). Since you've chosen the spot for hovering to be somewhere around the equator, as that's where the rotation velocity at the surface is approx. 1000mph, it would mean the still air is moving at that velocity w/r to the drone and the still air is perceived as 1000mph wind. Now, you could have some non-still air where the drone hovers, i.e. some local winds, that would change the perceived wind speed in either direction. But since there are no 1000mph winds even in the strongest hurricanes, you could never expect to nullify all that wind coming from the rotation of the atmosphere.
Of course you could have instead chosen a spot somewhere near the poles, where the rotation can be as leisurely as you want, including no rotation at all (at the poles). One can easily imagine some local wind patterns at least momentarily exactly matching the rotational velocity of the atmosphere so that your drone can hover in a

Hmm I'm not sure I get the concept of the entire atmosphere moving at the same speed and direction with earths rotation. If a jet flew against the rotation, at the equator, at 1000mph , would it face 2000mph head winds? Similarly if it flew with the spin at 1000mph would it then face zero head wind?

 

[PeroK]

Hmm I'm not sure I get the concept of the entire atmosphere moving at the same speed and direction with earths rotation.

I think we all see that you don't get that concept. But, if the Earth is spinning and the atmosphere wasn't, then you'd have $1600 \ km/h$ winds on the surface.

If a jet flew against the rotation, at the equator, at 1000mph , would it face 2000mph head winds? Similarly if it flew with the spin at 1000mph would it then face zero head wind?

Hmm That's precisely what would happen if the atmosphere were not spinning. You've got the whole thing the wrong way round.

 

[PeroK]

See here, for example:

https://www.sciencefocus.com/planet-earth/how-does-the-atmosphere-rotate-with-the-earth

 

[Baluncore]

Here is a map showing the wind speed at the surface.
https://earth.nullschool.net/#current/wind/surface/level/winkel3=1.95,0.03,234/loc=0.005,0.399

 

[Bandersnatch]

You're getting confused by the changing reference frames. It's normal.
Planes fly w/r to the wind, not the ground, and certainly not w/r to the Sun (or stars). That is to say, their engines have to work with the medium they're pushing against.

A plane at the equator flying against the rotation of the Earth at 1000mph would hover w/r to the Sun (it would appear to chase the Sun). But its pitot tube's windspeed measurements, and its engines, and any unfortunate hand stuck out of a window, would all agree that it's going at 1000mph. If there were no local wind w/r to the ground, the groundspeed would similarly be 1000mph.
If it flew at 1000mph with the rotation, it'd measure the same windspeed (again, it's flying through the air), and the same groundspeed (again, in otherwise windless conditions). But from a point of view of the background stars, it'd return to the point of origin (again, w/r to the Sun, not the ground) in half the time than an otherwise stationary point on the surface would. The 'day' between two sunrises on the plane would last 12h instead of 24. But from the point of view of passengers waiting at the airport it'd travel just as fast either way.

 

[Vic43]

The air is rotating with the planet. Wind is motion of the air w/r to the observer (here, the drone). Since you've chosen the spot for hovering to be somewhere around the equator, as that's where the rotation velocity at the surface is approx. 1000mph, it would mean the still air is moving at that velocity w/r to the drone and the still air is perceived as 1000mph wind. Now, you could have some non-still air where the drone hovers, i.e. some local winds, that would change the perceived wind speed in either direction. But since there are no 1000mph winds even in the strongest hurricanes, you could never expect to nullify all that wind coming from the rotation of the atmosphere.
Of course you could have instead chosen a spot somewhere near the poles, where the rotation can be as leisurely as you want, including no rotation at all (at the poles). One can easily imagine some local wind patterns at least momentarily exactly matching the rotational velocity of the atmosphere so that your drone can hover in a

I think we all see that you don't get that concept. But, if the Earth is spinning and the atmosphere wasn't, then you'd have $1600 \ km/h$ winds on the surface.

Hmm That's precisely what would happen if the atmosphere were not spinning. You've got the whole thing the wrong way round.

Yeah I guess you are right bout the fact if the atmosphere wasn't spinning at the same rate it'd be 1600kmph winds. Like I said I'm no physicist, just find it an interesting topic. It's a hard thing to grasp that the atmosphere is being pulled along with earth by friction as we can move so freely in it , and there are different local winds and weather patterns everywhere. I guess gravity is the thing that holds everything together and i was missing the fact that the atmosphere has weight/mass/particles that are affected by gravity . I think I find it easier to understand if I imagine the atmosphere as a solid lol. Anyway , I appreciate everyone's feedback.

 

[Vic43]

I'm still not sold on the explanations given about the counteracting of the inertia thing with the drone though (only using drone as an example as it can propel itself in a direction as well as hover) If a drone flew 2000mph against the spin at the equator it would have to fly for 1 hour to negate the inertia , if it then hovered relative to a star and the wind at that area was zero , the earth would have to spin under the drone at around 1000mph right? .....right? What am I (or you guys) not getting?

 

[PeroK]

I'm still not sold on the explanations given about the counteracting of the inertia thing with the drone though (only using drone as an example as it can propel itself in a direction as well as hover) If a drone flew 2000mph against the spin at the equator it would have to fly for 1 hour to negate the inertia

This makes no sense. The drone would fly 2000 miles. If its engines stopped, it would soon by back at rest relative to the atmosphere and spinning with the Earth again. This is because the atmosphere exerts a force on the drone whenever its moving. You must be misunderstanding the concepts of force and inertia.

, if it then hovered relative to a star and the wind at that area was zero , the earth would have to spin under the drone at around 1000mph right? .....right? What am I (or you guys) not getting?

The Earth is spinning, the atmosphere is spinning. The drone's motion must be relative to that. If the drone is not moving relative to the stars, then it must be moving relative to the surface and the atmosphere (except at or near the poles, of course).

 

[sophiecentaur]

once it flew far enough against earths spin to counter the inertia

You'd need to translate that into English / Physics if you want a meaningful response.

You would be describing the very hard task of keeping a flying machine flying West fast enough to keep the Sun overhead? (on the Equator, of course). Or maybe using a powerful fan to achieve the same thing.

From your posts above, I get the impression that you have argued yourself into a corner in an attempt not to be wrong. PF is not the one who's out of step here.

 

[Bandersnatch]

Inertia is the resistance to acceleration. What you have been conceptualising as countering here - the spin of the Earth - is velocity. In common parlance the distinction can be blurry.

When viewed from a non-rotating reference frame - here it means the point of view of the Sun and the background stars - a point at the surface of the Earth at the equator has some linear velocity. If you want the drone to hover above that point as seen from the non-rotating reference frame, it has to have equal but opposite velocity, in addition to its hovering action.
Once you impart that velocity through the use of some force (like the drone's engines), and in the absence of other forces (like drag from the atmosphere), it'll hover at that spot forever. This is Newton's first law of motion.
Inertia only comes into play here when the drone is accelerating to that velocity, as it determines how much force is required. This is Newton's second law. Inertia is the mass in F=ma.

So if what you need to hover w/r to the Sun at the equator is equal and opposite surface velocity, there's no point in ever going 2000mph. You just get to 1000mph and either cut the engines (if there's no drag) or keep firing them to maintain that velocity.
You'd only need more/less speed if you wanted to change where exactly you want to hover. Maybe you wanted the Sun to be directly overhead or something.

The case with an atmosphere is no different than swimming against the current in a river. You want to stay at rest w/r to the river banks, you swim as fast as the current does, only in the opposite direction. Any other speed will move you w/r to the banks. And if you stop swimming = applying force against drag of the medium you're in, the current will quickly carry you away.

 

[hmmm27]

What am I (or you guys) not getting?

Well, what I don't seem to be getting is relevant context when you use the words "hover" or "speed". Or, the relevance of anything to do with "inertia".

There's a difference between waiting for information and being confused.

Much the same as if I were standing on a conveyor belt I would move with it , but if I ran against it at the same speed I would be running on the spot while the belt moves under me.

Now, that's not confusing at all.

 

[Baluncore]

Now, that's not confusing at all.

Think about a long conveyer belt , there is a mid point marker.

That does not clearly specify, if the marker is on the moving belt material, or on the fixed frame, next to the moving belt. You must be more precise when there are multiple possible interpretations. You know what you mean, but we cannot read your mind.

 

[Vic43]

That does not clearly specify, if the marker is on the moving belt material, or on the fixed frame, next to the moving belt. You must be more precise when there are multiple possible interpretations. You know what you mean, but we cannot read your mind.

Apologies. Yep on a fixed frame next to the belt

 

[Vic43]

Inertia is the resistance to acceleration. What you have been conceptualising as countering here - the spin of the Earth - is velocity. In common parlance the distinction can be blurry.

When viewed from a non-rotating reference frame - here it means the point of view of the Sun and the background stars - a point at the surface of the Earth at the equator has some linear velocity. If you want the drone to hover above that point as seen from the non-rotating reference frame, it has to have equal but opposite velocity, in addition to its hovering action.
Once you impart that velocity through the use of some force (like the drone's engines), and in the absence of other forces (like drag from the atmosphere), it'll hover at that spot forever. This is Newton's first law of motion.
Inertia only comes into play here when the drone is accelerating to that velocity, as it determines how much force is required. This is Newton's second law. Inertia is the mass in F=ma.

So if what you need to hover w/r to the Sun at the equator is equal and opposite surface velocity, there's no point in ever going 2000mph. You just get to 1000mph and either cut the engines (if there's no drag) or keep firing them to maintain that velocity.
You'd only need more/less speed if you wanted to change where exactly you want to hover. Maybe you wanted the Sun to be directly overhead or something.

The case with an atmosphere is no different than swimming against the current in a river. You want to stay at rest w/r to the river banks, you swim as fast as the current does, only in the opposite direction. Any other speed will move you w/r to the banks. And if you stop swimming = applying force against drag of the medium you're in, the current will quickly carry you away.

I guess I have been using confusing language which made it hard for you guys to understand what I was talking about. I'm glad you got the concept anyway . Thanks for your detailed response