How does an object maintain constant velocity according to Newton's First Law?

Click For Summary

Discussion Overview

The discussion revolves around the interpretation of Newton's First Law of Motion, specifically addressing how an object can maintain constant velocity and the implications of initial forces applied to an object. Participants explore concepts related to motion, inertia, and reference frames, with a focus on theoretical and conceptual aspects rather than practical applications.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that according to Newton's First Law, an object will remain at rest or in constant motion unless acted upon by an external force, leading to questions about how an object begins to move initially.
  • Others argue that to achieve constant velocity, a force must have been applied at some point in the past to accelerate the object to that velocity.
  • One participant suggests that an object can be analyzed in a reference frame where it has always been moving, implying that the concept of "beginning to move" may not apply universally.
  • There is a discussion about the implications of assuming an object was at rest in the infinite past, with some participants questioning the validity of this assumption.
  • Another viewpoint is presented that objects could originate from matter with existing momentum, such as celestial bodies formed from a nebula, which complicates the notion of initial force application.
  • Participants note that there are indeed inertial frames where an object may always have had momentum, challenging the idea that a force must have been applied for it to be in motion.
  • Some participants reflect on historical perspectives, mentioning that before Newton, the understanding of motion was limited, and he introduced concepts that clarified how forces affect motion.

Areas of Agreement / Disagreement

Participants express differing views on whether an object must have been acted upon by a force to begin moving, with some asserting that it can always be considered to be in motion in certain reference frames. The discussion remains unresolved, with multiple competing interpretations of the implications of Newton's First Law.

Contextual Notes

Limitations include the dependence on the choice of reference frames and the assumptions about the initial state of objects. The discussion does not resolve the complexities surrounding the application of Newton's First Law to various scenarios.

Musica
Messages
3
Reaction score
0
Newton's first law says that when an object is at rest or moving in constant velocity, it will stay that way unless external force is applied. So, net force is zero.

What I don't get is on an object moving in constant velocity. How is the object begin moving? Is netforce applied initially before it reaches its constant velocity?
 
Science news on Phys.org
Musica said:
Newton's first law says that when an object is at rest or moving in constant velocity, it will stay that way unless external force is applied. So, net force is zero.

What I don't get is on an object moving in constant velocity. How is the object begin moving? Is netforce applied initially before it reaches its constant velocity?
How it got that way is not part of the first law of motion, but yes, to get something moving on, for example, a flat surface, you have to give it a push. If the surface is frictionless it just keeps moving. If you don't give it a push it just keeps sitting there.
 
Musica said:
How is the object begin moving?
The object itself doesn’t have to begin to do anything. You can analyze any object in a reference frame where it always has been moving.
 
  • Like
Likes   Reactions: Cruz Martinez
Consider a frictionless surface.
 
Musica said:
Is netforce applied initially before it reaches its constant velocity?
Yes, some force must have been applied to the object in it's past in order to accelerate it to the velocity which it presently has.
(In relation to the same given frame of reference)
 
Before Newton, people didn't know or realize that things could move on their own. He taught people that if something gets a push in one direction, it will need a push is the opposite direction to stop.
 
rootone said:
Yes, some force must have been applied to the object in it's past in order to accelerate it to the velocity which it presently has.
(In relation to the same given frame of reference)
Why would one assume that in the infinite past that the object was at rest in an arbitrarily selected frame of reference?
 
jbriggs444 said:
Why would one assume that in the infinite past that the object was at rest in an arbitrarily selected frame of reference?
Because it's unlikely that the moving object does have an infinite past.
It could of course be that the object was formed out of matter which already has momentum - like the solar system,
However the momentum in that case hasn't come from nothing, it's momentum that was previously included in a nebula, and now is included in the Sun.
 
Last edited:
rootone said:
It could of course be that the object was formed out of matter which already has momentum
What do you mean by "it could be"?. It is absolutely certain that there are inertial frames (infinitely many) where it always had momentum.
 
  • #10
Poor wording on my part, yes I agree there certainly are frames where an object always had momentum,
In relation to the original question," How is the object begin moving , Is net force applied initially before it reaches its constant velocity?",
I was trying to explain that if the object was motionless at one stage and now it isn't, then a force must have been applied to it.
On the hand an object which comes into existence in an already moving condition, and still is moving now, doesn't 'begin to move' and no force need have been applied to it since it started existing.
 
  • #11
rootone said:
In relation to the original question," How is the object begin moving , Is net force applied initially before it reaches its constant velocity?",
The correct answer to that question is, that the object doesn't have to begin moving. It is always moving in some inertial frames and Newtons 1st Law applies in all of them.
 
  • #12
Blackberg said:
Before Newton, people didn't know or realize that things could move on their own. He taught people that if something gets a push in one direction, it will need a push is the opposite direction to stop.
And rightly so, most objects on Earth stop moveing because of friction they don't need a push in the opposite direction to make them stop.Newton was probably referring to celestial bodies which would be a hard concept to grasp let alone explain at that time.
 

Similar threads

  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 62 ·
3
Replies
62
Views
4K
  • · Replies 14 ·
Replies
14
Views
8K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 17 ·
Replies
17
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
27K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K