How Does General Relativity Explain an Object Thrown Up Returning Back?

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Discussion Overview

The discussion revolves around understanding how general relativity explains the phenomenon of an object thrown upwards returning to the ground. Participants explore the nature of gravity, its representation in curved spacetime, and the implications of different trajectories, including circular and elliptical paths.

Discussion Character

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

Main Points Raised

  • Some participants express confusion about how gravity operates when an object is thrown vertically upwards and returns to the ground.
  • Others suggest that the trajectory of a vertically thrown object can be understood as following an elliptical path, with the possibility of orbiting if not interrupted by the ground.
  • A participant introduces the concept of geodesic paths in curved spacetime to explain the motion of thrown objects.
  • One participant emphasizes the importance of both space and time dimensions in understanding gravity within general relativity, suggesting that mass attraction is a key effect.
  • Another participant mentions the mathematical representation of gravitational acceleration in spacetime, describing how different types of motion appear in this framework.
  • A participant reiterates their understanding of gravity as an attractive force directed towards the Earth, linking it to the acceleration experienced by thrown objects.
  • One post diverges from the main topic, asking a different question about average speed, which is noted as unrelated to the discussion on gravity.

Areas of Agreement / Disagreement

Participants generally express varying levels of understanding regarding the explanation of gravity in general relativity, with some agreeing on the elliptical nature of trajectories while others remain uncertain about the implications of curved spacetime. The discussion does not reach a consensus on the best explanation for the phenomenon.

Contextual Notes

Some participants may have misconceptions about the role of space curvature alone in modeling gravity, while others highlight the necessity of considering time in this context. The discussion includes references to external resources for further exploration of the concepts presented.

Who May Find This Useful

This discussion may be useful for individuals interested in the conceptual foundations of general relativity, the nature of gravity, and the mathematical representations of motion in spacetime.

rajeshmarndi
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I could understand gravity involve in object revolving around a big mass as the path of the object is circular.

But couldn't understand how gravity is explained when an object thrown up returns back.
 
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hi rajeshmarndi! :smile:

are you also happy about an orbit where the path is elliptical?

when you throw an object almost vertically, it follows an arc of an ellipse until it hits the ground …

if the ground wasn't there, it would orbit in that ellipse forever​

when you throw an object exactly vertically, if the ground wasn't there, it would go up and down forever in a "flat ellipse" :wink:
 
rajeshmarndi said:
I could understand gravity involve in object revolving around a big mass as the path of the object is circular.

But couldn't understand how gravity is explained when an object thrown up returns back.

Geodesic path in curved spacetime for a vertical throw.
http://www.relativitet.se/spacetime1.html
 
thanks A.T, for providing the link also.
It was helpful what i was searching.
 
rajeshmarndi said:
thanks A.T, for providing the link also.
It was helpful what i was searching.
Here is an interactive version of that, where you can thow it up and let it fall into a tunnel through the planet:
http://www.adamtoons.de/physics/gravitation.swf
 
A convenient way to remember how gravitational acceleration looks in spacetime is, which summarizes some detailed mathematics, is (with time on one axis and space on two others):

constant velocity appears as a straight line,

constant linear acceleration appears as a smooth curve, (say. an freely falling object)

constant rotational acceleration appears as a corkscrew (say, the Earth rotating about the sun)
 
AT -

thanks again, its really a new way users like me to have a look at space-time curve.
 
rajeshmarndi said:
AT -

thanks again, its really a new way users like me to have a look at space-time curve.

The title of the thread suggests that you might have had the misconception that it's the curvature of space only, that models gravity in General Relativity. But in fact the time dimension is crucial to understand the key effect of gravity: mass attraction.

Have a look at this:
http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html
 
rajeshmarndi said:
I could understand gravity involve in object revolving around a big mass as the path of the object is circular.

But couldn't understand how gravity is explained when an object thrown up returns back.
I guess, that is acceleration due to gravity.When an object is thrown vertically up then,it come down it caused gravity . Gravity always attractive. And it always directed to the earth.
 
  • #10
i could not understan about this given problem.. " A car travels up a nill at a constant speed of 37 km/h & return down the hill at a constat speed of 66 km/h. Calculate the average speed for the whole trip."
Can somebody help me answer this?,,, thaks a lot...
 
  • #11
The last two posts seem to have missed the point completely- that this is about the General Relativity picture of gravity.

kyrdmenchou, please do NOT 'hijack' another person's thread to ask a completely different question. Your question has nothing at all to do with gravity. I will answer your question by p.m.
 

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