A gravity problem i came across.

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Discussion Overview

The discussion revolves around a scenario involving a space shuttle in orbit around a planet and the implications of energy conservation when the shuttle exits the orbit. Participants explore the relationship between gravitational forces, orbital mechanics, and energy changes during this process.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether energy has been created when a shuttle exits orbit at a higher speed than it entered, suggesting a potential violation of energy conservation principles.
  • Another participant proposes that the increase in speed may imply that fuel is being burned, thus transferring energy into kinetic energy, which raises questions about the initial conditions of the scenario.
  • A different viewpoint emphasizes that while a body in orbit is accelerating, it is primarily the direction of the velocity that changes rather than the speed itself, with minor variations due to orbital eccentricity.
  • One participant reiterates that the shuttle gains energy upon exiting the orbit, but this energy must be supplied externally, likely through fuel combustion, rather than occurring spontaneously.

Areas of Agreement / Disagreement

Participants express differing views on the nature of energy changes in the scenario, with some suggesting that external energy input is necessary while others explore the implications of orbital mechanics. The discussion remains unresolved regarding the initial question of energy creation.

Contextual Notes

Participants do not fully agree on the assumptions regarding the shuttle's energy state and the mechanics of its orbit, leading to varying interpretations of energy conservation in this context.

robert_jaas
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Hello!

Im sure we're all familiar with the fact that energy can't be created, only changed into diffrent states. However, I've been thinking about this scenario i find rather strange:
If a space-shuttle is put in orbit around a planet or object with large gravity, the shuttle will accelerate around it. When the speed is high enough the gravity-field will not be able to keep the shuttle in orbit, and it will be thrown out into space again.

My question is: Have energy been created? Since the shuttle have greater speed after leaving the orbit than when it entered the orbit.

Im sure my problem is somehow invalid, i just want to get this one out of my head.

Thanks!
 
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You say, "when the speed is high enough..." Aren't you implying that fuel is being burnt (and energy transferred into kinetic) in order to achieve the higher speed? Maybe I just don't understand the set-up.
 
I think you have the wrong idea. A body in orbit around another body is accelerating and acceleration is a change in velocity. However velocity is a vector, and it is the angle part of the velocity which is changing not the speed. The speed varies slightly because of the orbit eccentricity but the orbit doesn't change, apart from losing energy to friction etc.
 
robert_jaas said:
Hello!My question is: Have energy been created? Since the shuttle have greater speed after leaving the orbit than when it entered the orbit.

The shuttle will indeed have more energy, but YOU have to give it that energy. As Philip Wood said, probably by burning fuel. It's not just going to happen by itself spontaneously.
 
Ok, thanks for the help!
 

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