How would a man on earth appear from outer space

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Discussion Overview

The discussion explores how a person on Earth would appear to an observer in outer space, particularly focusing on the motion of a dropped ball and the effects of Earth's rotation. It includes questions about pseudo forces and their perceptibility in relation to gravity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a ball dropped from a person's hand would appear to move tangentially to Earth's spin from an outer space perspective.
  • Another participant explains that the perception of the ball's motion depends on the observer's reference frame, noting that a person in geosynchronous orbit would not see anything unusual.
  • There is a discussion about the Coriolis effect and centrifugal force, with one participant stating that these pseudo forces are felt indirectly through phenomena like tornadoes and the Earth's shape.
  • One participant claims that the centrifugal force due to Earth's rotation is too weak to be felt in the presence of gravity, being approximately 300 times weaker than gravitational force.
  • A later reply confirms that if the Earth is dark and the ball is illuminated, the observer would initially see the ball moving tangentially to the Earth's spin.

Areas of Agreement / Disagreement

Participants express multiple viewpoints regarding the appearance of the ball and the effects of pseudo forces, indicating that the discussion remains unresolved with competing perspectives on these concepts.

Contextual Notes

Participants mention the dependence on reference frames and the limitations in perceiving weak forces, but do not resolve these complexities.

vijay_singh
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Hi

I was reading a general physics book and wondered how would a man on Earth appear to somebody watching from outer space.
Say for example a man on Earth just drops a ball from his hand, will it appear to somebody watching from outer space, as if the ball is released tangent to the spin of the earth?

I hope my question makes sense!

Another question, why don't we feel the pseudo force due to the Earth's rotation on its axis? or is it too weak?
 
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We do feel pseudo forces. That's why tornados and hurricanes (but not toilets) spin different directions in different hemispheres (because of the fictitious Coriolis force) and why the Earth is kinda like a squashed sphere not a perfect sphere (centrifigal force). In general these fictitious forces emerge when we assume we are in a stationary reference frame but actually are in a rotating one (see http://en.wikipedia.org/wiki/Rotating_reference_frame). However, how we look to a person in space is ENTIRELY dependent on what the reference frame of the person is. For example, if the person was in geosynchronous orbit they wouldn't see anything odd.
 
vijay_singh said:
Another question, why don't we feel the pseudo force due to the Earth's rotation on its axis? or is it too weak?
It is too weak to be felt, in the presence of gravity. More precisely, it's about 300 times weaker than gravity (at the equator), and a human can't pick out that 1-in-300 difference. If there were no gravity, you'd probably be able to feel the centrifugal force, though; about 1.5-2 N on an average adult.
 
Last edited:
Hi vijay! :smile:
vijay_singh said:
Say for example a man on Earth just drops a ball from his hand, will it appear to somebody watching from outer space, as if the ball is released tangent to the spin of the earth?

Yes, if the Earth is dark (because it's night), but the ball is lit, then all the watcher will initially be able to see is the ball moving tangent to the spin of the earth, as you say. :smile:
 
Thank you all for responding and confirming the answers.
 

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