How velocity builds up in space

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    Space Velocity
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Discussion Overview

The discussion explores how velocity builds up in space, particularly in the context of Newton's laws of motion and the behavior of rockets in a near-frictionless environment. Participants examine the implications of these laws in space travel, acceleration, and the measurement of velocity and kinetic energy.

Discussion Character

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

Main Points Raised

  • Some participants assert that Newton's first law applies in space, suggesting that an object will maintain its velocity unless acted upon by an external force.
  • One participant notes that momentum is conserved when considering the rocket's mass including expelled fuel, indicating that chemical energy converts into kinetic energy.
  • Another participant explains that while velocity can build in space due to gravitational forces, a rocket will continue at its achieved velocity in the absence of friction and other forces.
  • There is a discussion about the relativity of motion, with one participant stating that without nearby objects for comparison, distinguishing between different states of motion becomes complex.
  • Some participants agree that continuous force application on a rocket will lead to ongoing acceleration, as there is no terminal velocity in the absence of resistance.
  • A question is raised about the possibility of an object being completely still in space and how one might measure its kinetic energy, leading to a discussion on the relativity of velocity and kinetic energy measurement.
  • One participant introduces the idea that at high speeds, special relativity may alter the rules that apply at lower speeds, suggesting a potential limitation of Newtonian mechanics.

Areas of Agreement / Disagreement

Participants generally agree on the application of Newton's laws in space and the concept of continuous acceleration without resistance. However, there is no consensus on the implications of high-speed motion and the transition to special relativity, indicating ongoing debate.

Contextual Notes

Some assumptions about the absence of external forces and the nature of motion in space are not fully explored, and the discussion includes varying interpretations of how velocity and acceleration are perceived in a relativistic context.

lpbug
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According to Newton's first law of motion: "An object at rest will remain at rest and an object at motion will remain at a constant velocity unless acted upon by an external force."
I was just wondering if this law applies to space; since there are no friction in air and little to no gravity, I was just wondering if velocity could build up in space. For example, I shot a rocket into outer space and the more velocity I add to it the faster it goes and even if I take out the source of propulsion, it'll still travel as fast as I set it without ever slowing down.
Thanks for answering!
 
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If you include the spent fuel expelled by the rocket's engine as part of the rocket's mass, there are no external forces, and momentum is conservered. However chemical energy is converted into kinetic energy, most of this into the fuel which ends up with a very high velocity with respect to the rocket engine.
 
In general, Newton's laws apply in space as here on earth. gravity, friction, and other forces may vary, but the LAWS remain intact.

"I was just wondering if this law applies to space; since there are no friction in air and little to no gravity, I was just wondering if velocity could build up in space..."

Velocity can build in space due to F = MA and V=AT as a body approaches a planet for example...where gravity exerts a force on the body and the body accelerates. This effect can be ustilized to good effect in space probes where the "slingshot effect" can be used to speed up vehicles.


"For example, I shot a rocket into outer space and the more velocity I add to it the faster it goes and even if I take out the source of propulsion, it'll still travel as fast as I set it without ever slowing down."

If you assume no friction in space then one view is that there are no forces to slow it down. In fact space is curved by gravity in different places,more so near large masses like stars, so over time the rocket will turn and follow gravitational curves a bit,,,if you ignore these, it will retain a constant fixed "straiht line" velocity.

Once the rocket engine is turned off in free space, no friction and no other forces, the rocket will continue at the velocity achieved...it won't slow down nor speed up because there are no additional forces acting...restart the rocket engine...apply a force... acceleration ensures and velocity increases...
 
As a matter of fact, in the extremely low friction environmentthe two parts of this law become one. If you put yourself in the Rockets place, with no nearby objects against which to compare yourself, you will find that you're able to tell the difference between "accelerating" and "not accelerating," but the difference between "moving very fast at a constant velocity," "moving very slowly at a constant velocity," and "sitting still" will require you to ask, "compared to what?"

So, moving at a constant velocity literally is remaining at rest.
 
Ok... well, so if i keep on exerting force upon the "rocket" I can achieve a build-up in the rocket's velocity right? So it'll keep on going faster and faster... is that correct?
 
Yes, that is correct. Without wind resistance, there is no "terminal velocity." As long as you keep pushing, the rocket (or any object) will keep accelerating.
 
A semi-related question: Is it possible to get something to stand completely still out in space? I'm not talking about on the lowest level, I know there'll always be some movement there, but larger objects. Would there be anyway to tell if an object didn't move at all, considering everything else in space is moving? Some way to measure an object's kinetic energy perhaps?
 
Since velocity can only be measured with respect to other objects, so too, kinetic energy.
 
wait but it builds up right? I mean it will buld up like:
i start out 20Mph and slowly i will accelerate to 100mph and keep adding up right?
 
  • #10
lpbug said:
wait but it builds up right? I mean it will buld up like:
i start out 20Mph and slowly i will accelerate to 100mph and keep adding up right?
Hmm, yes.

I think I can see where your going with this...
 
  • #11
...the rules that work at low speed start breaking down at high speed. Special Relativity takes over for Newtonian mechanics.
 

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