Is a Helicopter on a Geostationary Orbit?

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Discussion Overview

The discussion centers on whether a helicopter that remains stationary relative to the Earth's surface can be considered to be in a geostationary orbit. Participants explore the definitions of orbit, the forces acting on a helicopter compared to those on a satellite, and the implications of these forces on the concept of being in orbit.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants argue that a helicopter is not in orbit because it is not in free fall, unlike a satellite, which follows a gravitational path around the Earth.
  • Others suggest that if a helicopter hovers for an extended period, its trajectory could be seen as circular, similar to a geostationary satellite, though they acknowledge that this does not constitute an orbit.
  • One participant points out that both a satellite and a helicopter experience centripetal forces due to their weight, but emphasizes that the helicopter's lift counteracts its weight, preventing it from being in orbit.
  • Another participant clarifies that the definition of orbit relates to the gravitational interaction with Earth, not merely the position relative to the surface.
  • There is a discussion about the net forces acting on objects in circular motion, with some participants questioning how an object can travel in a circle if the net force is zero.
  • Several participants express uncertainty about the implications of forces acting on a helicopter and how they relate to the concept of orbit.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether a helicopter can be considered in a geostationary orbit. There are multiple competing views regarding the definitions and implications of orbit, forces, and motion.

Contextual Notes

Limitations in the discussion include varying interpretations of the term "orbit," the role of different forces acting on the helicopter, and the implications of these forces on circular motion. Some participants express confusion about the relationship between net force and circular motion.

  • #31
A.T. said:
No, they don't always act along the same line. The gravitational force is not perpendicular to the surface (except at the poles and equator). The rest of your argument is based on this misconception.

The force from the chair includes a static friction force that opposes any component of gravity or centripetal force that is tangent to the Earth's surface. The result is that the chair does exert a force exactly opposite to all other lateral forces on your body.
 
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  • #32
FactChecker said:
The force from the chair includes a static friction force that opposes any component of gravity or centripetal force that is tangent to the Earth's surface. The result is that the chair does exert a force exactly opposite to all other lateral forces on your body.
No matter how you decompose them into components, the vector sum of gravity and chair force on you is not zero. If it was, you would move in a straight line in the inertial frame, but you move in a circle.

So no, the component of gravity tangent to the surface is not canceled by static friction. And neither is the component of gravity normal to the surface completely canceled by the normal force. These unbalanced components provide together the centripetal force to keep you on a circular trajectory.
 
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  • #33
A.T. said:
So no, the component of gravity tangent to the surface is not canceled by static friction. And neither is the component of gravity normal to the surface completely canceled by the normal force. These unbalanced components provide together the centripetal force to keep you on a circular trajectory.

Regarding the lateral force: The reason a person does not slide laterally is that the static friction exactly cancels any lateral force. Static friction does that. I know. I have gotten it wrong in simulations and watched as the simulated object of interest slowly started to slide laterally.

Regarding the normal force: You are right about there being some acceleration. At no point does a person come closer to the center of the earth. The chair provides the exact force necessary to make that happen. All the forces are constantly rotating except at the geographical poles.
 
  • #34
A body in orbit is in free fall.
 
  • #35
FactChecker said:
The reason a person does not slide laterally is that the static friction exactly cancels any lateral force.
No, the component of gravity tangent to the surface is not exactly canceled by static friction.
 
  • #36
A.T. said:
No, the component of gravity tangent to the surface is not exactly canceled by static friction.

In a perfect world, the surface of the Earth is an equipotential surface where both gravity and centripetal force are take into account. In that case there is no lateral force component tangent to the surface. In a realistic world, there are small lateral forces but static friction stops things from sliding around. The force from static friction is the exact amount needed to counteract other forces that are too small to overcome the static friction. But this is digressing from the OP.
 
  • #37
Can we focus on the original question, please?
 
  • #38
I am surprised that no one has used Keplers law to compute the orbital period for a orbit at the Earth's surface.
 
  • #39
Vanadium 50 said:
Can we focus on the original question, please?
Since that apparently could not be done, thread closed.
 

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