B How do I know in which direction an object is moving?

[John Mcrain]

How do I know is this object at rest,moving to the left or moving to the right ?

 

[Dale]

If it were moving left is it at rest? If it were moving right is it at rest? What do you conclude?

 

[John Mcrain]

If it were moving left is it at rest? If it were moving right is it at rest? What do you conclude?

If it were moving to the left then is not at rest,if it were moving right than is not at rest...

 

[Ibix]

I think your word order was not quite correct and your question may have been misunderstood. I think the question is, "how can I tell if this object is at rest, moving to the left, or moving to the right".

If you are on a train, what clues are there that you are moving?

 

[John Mcrain]

I think your word order was not quite correct and your question may have been misunderstood. I think the question is, "how can I tell if this object is at rest, moving to the left, or moving to the right".

If you are on a train, what clues are there that you are moving?

My friend look at this object and say: this object can only stay at same position,he said imagine two mens pulls same object with rope with same force in opposite direction,so object must be at rest.

But if this object is plane ,and red force is drag and blue is thrust ,than object moving to the right..

So it seems we don't know from forces vector,what happening with this object..

Is now clear where confusion comes?

 

[A.T.]

How do I know is this object at rest,moving to the left or moving to the right ?

View attachment 277257

How the object is moving depends on the reference frame you use.

 

[John Mcrain]

How the object is moving depends on the reference frame you use.

I draw refernece frame origin in my picture

 

[A.T.]

My friend look at this object and say: this object can only stay at same position,he said imagine two mens pulls same object with rope with same force in opposite direction,so object must be at rest.

Are you asking about the rest frame of the object, before any forces were applied?

Is now clear where confusion comes?

No.

 

[John Mcrain]

Are you asking about the rest frame of the object, before any forces were applied?No.

My friend look at this object and say: this object can only stay at same position,he said imagine two mens pulls same object with rope with same force in opposite direction,so object must be at rest.

But if this object is plane ,and red force is drag and blue is thrust ,than object moving to the right..

So it seems we don't know from forces vector,what happening with this object..

 

[A.T.]

My friend look at this object and say: this object can only stay at same position,he said imagine two mens pulls same object with rope with same force in opposite direction,so object must be at rest.

You didn't answer my question: Are you asking about the rest frame of the object, before any forces were applied?

But if this object is plane ,and red force is drag and blue is thrust ,than object moving to the right..

Depends on the reference frame.

So it seems we don't know from forces vector,what happening with this object..

Just use Newtons 2nd Law. And stop asking about movement without specifying the reference frame. It's a meaningless question.

 

[John Mcrain]

You didn't answer my question: Are you asking about the rest frame of the object, before any forces were applied?

Because I don't understand your question.
Do you see where is origin on my reference frame in my picture,what else I need to draw?

 

[John Mcrain]

You didn't answer my question: Are you asking about the rest frame of the object, before any forces were applied? Depends on the reference frame.Just use Newtons 2nd Law. And stop asking about movement without specifying the reference frame. It's a meaningless question.

Imagine human eyese is at origin of frame and looking at this object..
What happened with this object from human perspective?

 

[Dale]

I think your word order was not quite correct and your question may have been misunderstood. I think the question is, "how can I tell if this object is at rest, moving to the left, or moving to the right".

If you are on a train, what clues are there that you are moving?

Oops, then I misunderstood the question. My apologies @John Mcrain

 

[Dale]

So it seems we don't know from forces vector,what happening with this object..

Is now clear where confusion comes?

That is correct. From the forces you only know the acceleration. You cannot determine the velocity from the forces alone. In fact, the object could even be moving up or down.

In order to determine the motion completely in addition to the forces you must also specify the initial conditions: the initial position and the initial velocity.

 

[John Mcrain]

I think your word order was not quite correct and your question may have been misunderstood. I think the question is, "how can I tell if this object is at rest, moving to the left, or moving to the right".

If you are on a train, what clues are there that you are moving?

No.
Object is train and I am at train station looking at this train(object).
What is movement of train(object)?

 

[John Mcrain]

That is correct. From the forces you only know the acceleration. You cannot determine the velocity from the forces alone. In fact, the object could even be moving up or down.

In order to determine the motion completely in addition to the forces you must also specify the initial conditions: the initial position and the initial velocity.

How is possible to object moves up and down if forces act only left and right?

Initial positon is at this place like its drawn at picture and initial velocity is zero in relation to origin at picture..

 

[kuruman]

How do I know is this object at rest,moving to the left or moving to the right ?

View attachment 277257

If this object is in a car with you and you are driving on the highway at 50 miles/hour, you will say that the object is not moving.
If you are driving on the highway at 50 miles/hour, and this object is hanging from a tree branch on the side of the road, you will say that the object is moving.

How do you know that it is not moving in the first case and is moving in the second case?

 

[Dale]

How is possible to object moves up and down if forces act only left and right?

If its initial velocity were up then it would continue to move up at the same speed even with forces only left and right.

Initial positon is at this place like its drawn at picture and initial velocity is zero in realtion to origin at picture..

Then it starts at rest and remains at rest. It does not move. Is that clear why? There is no net force to cause it to accelerate. Since it doesn't accelerate its velocity doesn't change. Since its velocity starts at zero and doesn't change then it stays at zero. Since its velocity is zero it is at rest.

Forces produce acceleration, not velocity. That was Newton's key insight over Aristotle.

 

[John Mcrain]

If its initial velocity were up then it would continue to move up at the same speed even with forces only left and right.

Then it starts at rest and remains at rest. It does not move. Is that clear why? There is no net force to cause it to accelerate. Since it doesn't accelerate its velocity doesn't change. Since its velocity starts at zero and doesn't change then it stays at zero. Since its velocity is zero it is at rest.

Forces produce acceleration, not velocity. That was Newton's key insight over Aristotle.

Ok thanks for answer,so answer on my qestion lie in inital conditions.

So if inital conditions was moving to the right at 100km/h,then object is still moving to the right at 100km/h?

 

[Dale]

Ok thanks for answer,so answer on my qestion lie in inital conditions.

So if inital conditions was moving to the right at 100km/h,then object is still moving to the right at 100km/h?

Yes! Exactly

 

[russ_watters]

This is Newton's first law.

 

[John Mcrain]

Again we have lotsf post to get answer..

Obviusly my english is so bad?

 

[A.T.]

... initial velocity is zero in relation to origin ...

Then in that frame it will remain zero.

 

[Herman Trivilino]

My friend look at this object and say: this object can only stay at same position,he said imagine two mens pulls same object with rope with same force in opposite direction,so object must be at rest.

Couldn't they produce the same results by doing this on a moving train?

 

[sophiecentaur]

How do I know is this object at rest,moving to the left or moving to the right ?

It's not marked on the diagram so you don't know.

This is Newton's first law.

I was wondering why it took so long for someone to quote Sir Isaac.