Newton's First Law: Movement in Space Without Friction

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Discussion Overview

The discussion revolves around Newton's First Law of Motion, specifically addressing the movement of spacecraft in the absence of friction and the role of external forces such as gravity. Participants explore the implications of these concepts in the context of space travel and rocket propulsion.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant asserts that everything should move in a straight line if there is no friction, questioning why rockets need fuel to maintain motion in space.
  • Another participant clarifies that a spacecraft would indeed travel in a straight line if no forces, such as gravity, are acting on it.
  • A different participant challenges the initial claim, stating that movement in a straight line is contingent on the absence of external forces, not just friction.
  • It is noted that Newton's First Law states that an object continues in its state of motion unless acted upon by an external force, which includes but is not limited to friction.
  • One participant points out that an object can move in a straight line even with a force acting on it, provided the force aligns with the direction of motion.
  • A participant raises a question about the trajectory of a satellite, explaining that rockets adjust their thrust direction to change their path after launch.

Areas of Agreement / Disagreement

Participants express differing interpretations of Newton's First Law, particularly regarding the role of friction and external forces in determining motion. There is no consensus on the initial claims about movement in space.

Contextual Notes

Some statements rely on specific interpretations of Newton's laws, and the discussion includes various assumptions about forces acting on objects in space. The mathematical relationship described by Newton's second law is mentioned but not fully explored.

avito009
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Everything should move in a straight line if there is no friction. But when an aircraft goes into space it needs to move burning its fuel. Why does it not move constantly in straight line?

So is the reason behind the fact that a rocket needs to be propelled, that the gravity of the sun and other planets does not allow it to move in straight line without fuel?
 
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A spacecraft would travel in a straight line if there were no forces acting on it (eg no gravity from a star/planet).
 
avito009 said:
Everything should move in a straight line if there is no friction
Where did you hear that?
 
avito009 said:
Everything should move in a straight line if there is no friction.

That's not right. Everything should (and does) move in a straight line if there is no external force acting on it. Friction is just one of the many forces that might act to push an object off its inertial trajectory.

And in fact, just as Newton's first law says that an object not experiencing any external forces moves in a straight line at a constant velocity, Newton's second law says that if there is an external force at work, the object will not move in a straight line at a constant velocity - mathematically we have ##F=ma##.
 
first law states that every objects in the universe continues in its state of motion unless an external force act on it. it doesn't mean friction.
 
Note that an object can still move in a straight line with a force acting on it, the force would just be in the same or opposite direction that the object is already traveling in and would just accelerate or decelerate the object.
 
avito009 said:
But when an aircraft goes into space it needs to move burning its fuel. Why does it not move constantly in straight line?

Are you thinking of when a satellite is launched, it starts out going straight up, then curves into a horizontal path? That is done by rotating the rocket engines slightly so as to change the direction of thrust.
 

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