Equations of motion the conditions

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Discussion Overview

The discussion revolves around the conditions necessary for the application of the equations of motion, particularly focusing on uniform acceleration and the context of inertial frames. Participants explore various aspects of these conditions, including the implications of relativistic speeds and the need for initial conditions.

Discussion Character

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

Main Points Raised

  • Some participants assert that the equations of motion require uniform acceleration and that they are applicable only in inertial frames.
  • Others mention that small velocities compared to the speed of light are necessary for the Newtonian equations to be valid, highlighting the breakdown of these equations at relativistic speeds.
  • There is a discussion about the meaning of an inertial frame, with some defining it as a non-rotating frame.
  • One participant suggests that initial conditions, such as initial position and velocity, are also essential for using the equations of motion.
  • Some participants express confusion over the terminology and the relevance of non-inertial frames in the context of the original question.
  • A later reply emphasizes the need to identify given quantities when solving problems related to equations of motion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specific conditions for applying the equations of motion. There are competing views regarding the relevance of relativistic effects and the interpretation of inertial frames, leading to some confusion and debate.

Contextual Notes

Participants mention the need for clarity regarding initial conditions and the implications of relativistic speeds, but there is no resolution on how these factors universally affect the application of the equations of motion.

jeekeshen
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Equations of motion! the conditions pleasezz

What are the conditions that enable the equations of motion to be used except from the fact that acceleration must be uniform ?
 
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jeekeshen said:
What are the conditions that enable the equations of motion to be used except from the fact that acceleration must be uniform ?

Small velocities compared to the speed of light and an inertial frame.
 


Inertial frame ? meaning wat ?
 


Not rotating
 


Uniform acceleration compensate the rotating phenomenon as well i think !
 


jeekeshen said:
Uniform acceleration compensate the rotating phenomenon as well i think !

If you sit in a train traveling at steady speed (inertial frame) and toss a ball to a friend he can catch it - no problem.

If you both are on a ship in a storm, wildly, suddenly changing direction OR you both sit on a children's 'roundabout' while it's spinning (both non-inertial frames) you will find it nearly impossible. The laws of motion for the non-inertial frame will be different from those you are used to.

You may be able to compensate by adding in some complicated motion of your own - but that isn't the point.
 


@OP:

I think you meant to ask about initial conditions. You still need to know the initial position and the initial velocity of the particle.
 


ya that's wat i meant the initial conditions :S.. just like acceleration should be uniform, many questions ask too but the other one that speed must be less than speed of light is too obvious else the matter will disintegrate :S
 
  • #10


jeekeshen said:
many questions ask too but the other one that speed must be less than speed of light is too obvious else the matter will disintegrate :S

No,what I meant is that the velocity of the object must be significantly smaller then the velocity of light for the Newtonian equations of motion to work. At velocities that are a significant fraction of c, those equations do not work due to relativistic effects.There is also no reason for matter to disintegrate at speeds close to c.
 
Last edited:
  • #11


Dickfore said:
I think you meant to ask about initial conditions.
No he didn't (now he thinks he does!) He barely speaks English - doesn't understand what you mean - you just confused him.
 
  • #12


AJ Bentley said:
No he didn't (now he thinks he does!) He barely speaks English - doesn't understand what you mean - you just confused him.

Lol, I confused him and not you with talks about non-inertial reference frames and speed of light.
 
  • #13


Dickfore said:
with talks about non-inertial reference frames and speed of light.
Look to see who's saying what before you post. I never mentioned either except to explain in detail what a non-inertial frame is.
 
  • #14


Dickfore said:
Lol, I confused him and not you with talks about non-inertial reference frames and speed of light.

:smile:
I am sorry If I confused him. I consider that position and velocity are info necessary to using the equations not something that restrains their validity.That is what I thought he was asking.

AJ Bentley said:
Look to see who's saying what before you post. I never mentioned either except to explain in detail what a non-inertial frame is.
Yeah blame poor old bp.
 
  • #15


AJ Bentley said:
Look to see who's saying what before you post. I never mentioned either except to explain in detail what a non-inertial frame is.

Who asked you to explain anything? You assumed that this is the question he was asking and proceeded with your own answer. This is the same thing I did. So, please, don't tell me what he meant or he didn't mean.
 
  • #16


Dickfore said:
You assumed that this is the question he was asking

And I quote. From the OP.

Inertial frame ? meaning wat ?

To which I answered 'not rotating'

Simple question and direct answer.
 
  • #17


AJ Bentley said:
And I quote. From the OP.

Inertial frame ? meaning wat ?

To which I answered 'not rotating'

Simple question and direct answer.

Do you mean the original poster or the original post when you say OP? It is obvious he was confused as hell by that point so he used 'wat'.

Also, your answer is not correct, but that's not the topic of discussion in this thread
 
  • #18


But he only asked that in response to bp-psy's response
"Small velocities compared to the speed of light and an inertial frame."
to a question that asked only about the "equations of motion" and said nothing about relativity.
 
  • #19


HallsofIvy said:
But he only asked that in response to bp-psy's response
"Small velocities compared to the speed of light and an inertial frame."
to a question that asked only about the "equations of motion" and said nothing about relativity.
He said nothing about relativity but he didn't specifically asked to ignore it.I think that my answer was valid considering how the question was formulated. Anyway feel free to delete all posts up to the op since I see this thread got ugly.
 
  • #20


Jeekeshan let me try to summarise.There are equations of linear motion and also equations of circular motion.The two sets of equations are analogous.I am assuming that you are referring to linear motion.The conditions necessary to use these equations is that the object must be moving in a straight line with uniform acceleration but I think you already know this.The equations break down as light speeds are approached so this places some limitations on their use.With equations of linear motion there are five quantities which are relevant and these are often given the symbols u,v,a,t and s.The symbols you use may be different.In order to solve a problem you need to be given three of the five quantities.Strangely,identifying what three quantities are given sometimes proves to be the most difficult part of the problem.First you need to identify the given quantities then select the right equation(s) to find the unknown(s) and then plug the numbers in.
 
  • #21


Yes I've understood that but in some questions they ask conditions for the application of these equations of motion. I know the fact of the speed of light and that of uniform acceleration but i wanted some more that appears to seem more general.
 

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