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

• B
• John Mcrain
In summary, the motion of an object cannot be determined solely from the forces acting on it. Initial conditions, such as the object's initial position and velocity, must also be considered.
John Mcrain
How do I know is this object at rest,moving to the left or moving to the right ?

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

Dale said:
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...

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?

Ibix said:
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?

John Mcrain said:
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.

A.T. said:
How the object is moving depends on the reference frame you use.
I draw refernece frame origin in my picture

John Mcrain said:
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?

John Mcrain said:
Is now clear where confusion comes?
No.

A.T. said:
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..

Motore
John Mcrain said:
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?

John Mcrain said:
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.

John Mcrain said:
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.

A.T. said:
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?

A.T. said:
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?

Ibix said:
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

John Mcrain said:
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.

lomidrevo
Ibix said:
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)?

Dale said:
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..

John Mcrain said:
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?

John Mcrain said:
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.

John Mcrain said:
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.

lomidrevo and russ_watters
Dale said:
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?

davenn
John Mcrain said:
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

This is Newton's first law.

sophiecentaur
Again we have lotsf post to get answer..

Obviusly my english is so bad?

John Mcrain said:
... initial velocity is zero in relation to origin ...
Then in that frame it will remain zero.

John Mcrain said:
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?

John Mcrain said:
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.
russ_watters said:
This is Newton's first law.
I was wondering why it took so long for someone to quote Sir Isaac.

## 1. How do I determine the direction an object is moving?

To determine the direction an object is moving, you can use the concept of vectors. A vector is a quantity that has both magnitude (size) and direction. By measuring the displacement of the object over a period of time, you can calculate the velocity vector and determine the direction of motion.

## 2. Can I use the position of an object to determine its direction of motion?

Yes, you can use the position of an object to determine its direction of motion. By comparing the position of the object at different points in time, you can calculate the displacement and determine the direction of motion. However, this method may not be as accurate as using the velocity vector.

## 3. How does the direction of motion affect an object's velocity?

The direction of motion is a crucial component of an object's velocity. Velocity is a vector quantity, meaning it has both magnitude and direction. Therefore, even if an object is moving at the same speed, a change in direction will result in a change in velocity.

## 4. Can an object change direction without changing its velocity?

Yes, an object can change direction without changing its velocity. This is known as uniform circular motion, where the object moves in a circular path at a constant speed. In this case, the velocity vector is constantly changing, but the magnitude of the velocity remains constant.

## 5. How can I determine the direction of motion without knowing the object's speed?

You can determine the direction of motion without knowing the object's speed by using the concept of relative motion. If you observe the object from a different reference frame, you can compare its position at different points in time and determine the direction of motion. However, to calculate the speed, you will need to know the distance and time taken by the object to travel that distance.

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