Helicopter Hovering: Solving the Mystery of Earth's Rotation

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    Helicopter Hovering
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Discussion Overview

The discussion centers around the question of why a helicopter hovering above the Earth does not drift away due to the planet's rotation. Participants explore the implications of inertia, momentum, and the role of the atmosphere in maintaining the helicopter's position relative to the Earth's surface.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that a helicopter retains its horizontal momentum when it lifts off, thus maintaining the same horizontal speed as the Earth's surface.
  • Others argue that the helicopter would need to move at a very small speed to "keep up" with the Earth's rotation, particularly at different altitudes.
  • A participant mentions Galileo's experiment with dropping balls from a ship to illustrate the concept of inertia, suggesting that the helicopter will maintain its velocity unless acted upon by an external force.
  • There is a discussion about the need for the helicopter to maintain its initial rotational speed imparted by the Earth, with specific speeds mentioned for different locations.
  • One participant notes that if the helicopter rises high enough, the curvature of the Earth could affect its position, requiring it to adjust its speed slightly to stay aligned with the Earth's rotation.
  • Another participant briefly mentions the influence of wind as a factor that could affect the helicopter's hovering stability.

Areas of Agreement / Disagreement

Participants generally agree on the concept of inertia and momentum but express differing views on the specifics of how a helicopter would need to adjust its speed to remain stationary relative to the Earth's surface. The discussion remains unresolved regarding the exact dynamics involved.

Contextual Notes

The discussion includes assumptions about the effects of the atmosphere and the curvature of the Earth, which are not fully explored or resolved. The varying speeds mentioned depend on specific geographic locations and altitudes.

Who May Find This Useful

This discussion may be of interest to those exploring concepts in physics related to motion, inertia, and the effects of Earth's rotation on objects in the atmosphere.

pr1de
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Question that was always bugging me.

Why doesn't a helicopter which could theoretically hover on the spot for hours doesn't end up in another part of the world. Since it's off from the ground doesn't it lose the velocity of Earth's rotation? What keeps it in the same place/at same velocity all the time? I would assume that it's the atmosphere that's rotating along with the planet right?
 
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Welcome to PF!

Hi pr1de! Welcome to PF! :wink:
pr1de said:
… Since it's off from the ground doesn't it lose the velocity of Earth's rotation?

No … imagine a hovercraft on the Moon (obviously, a helicopter wouldn't work there … no air! :biggrin:) …

it'll still hover! :smile:

The helicopter has horizontal momentum when it's on the ground.

When it lifts off, the only force is vertical, so it still has the same horizontal momentum: its horizontal speed still perfectly matches that of the Earth's surface. :wink:
 
If the 'copter was hovering at 100m above the Earth, to a rough approximation it would only need to move at about 0.01 mph to "keep up with" the rotation beneath it.
 


tiny-tim said:
Hi pr1de! Welcome to PF! :wink:


No … imagine a hovercraft on the Moon (obviously, a helicopter wouldn't work there … no air! :biggrin:) …

it'll still hover! :smile:

The helicopter has horizontal momentum when it's on the ground.

When it lifts off, the only force is vertical, so it still has the same horizontal momentum: its horizontal speed still perfectly matches that of the Earth's surface. :wink:

Increasing its distance from the centre means that its horizontal velocity (or angular velocity) must be less if its angular momentum remains the same.
 
I think Galileo tested that assumption by dropping balls from the mast of a ship and found they dropped straight down relative to the ship, not the earth. Newton explained it by saying that objects tend to remain as they are, either in motion or stationary. This he called inertia. The helicopter has the same velocity as the surface of the Earth and will keep that velocity unless something causes that velocity to change.
 
Stonebridge said:
If the 'copter was hovering at 100m above the Earth, to a rough approximation it would only need to move at about 0.01 mph to "keep up with" the rotation beneath it.

Well, yes but first it would have to keep its rotation imparted to it from the Earth, which is 1000mph at the equator and ~707mph up near the the great Lakes.

The OP's question is a bit vague so it's hard to tell why he thinks the helicopter would not stay stationary wrt the ground.
 
DaveC426913 said:
Well, yes but first it would have to keep its rotation imparted to it from the Earth, which is 1000mph at the equator and ~707mph up near the the great Lakes.

The OP's question is a bit vague so it's hard to tell why he thinks the helicopter would not stay stationary wrt the ground.

Yes, 1000mph at the equator, and approx 1000.01 mph at a height of 100m would be necessary to keep up with the Earth below.
ie, to maintain the same angular velocity.
 
So, the total answer is:
1] While parked, the helicopter has momentum imparted to it from the ground. At the equator, this is 1000mph.
2] When it lifts off, it retains this momentum, and continues moving at 1000mph.
3] If the helicopter were to lift high enough off the ground that the curvature of the Earth became a factor, then the Earth would be able to move under the copter slightly faster and the copter would fall behind (just like a race car one curve in the outside lane will fall behind). The copter would have to move very slightly to "keep pace" with the Earth.
4] This assumes we ignore the effect of the atmosphere. The atmo is carried along with the Earth, even at altitude. Which means as the copter rises, the atmo will overwhelm this tiny force of angular momentum.
 
Thank you guys, it all makes sense to me now. It's always good to have someone confirm your thoughts :D
 

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