Answer: Basic Physics Question - Free Fall in 2D or 3D?

In summary: Thanks for your input.My basic problem is that I don't understand what "falling in 3D" means. Are you saying that an object that falls in 3D is falling from all directions at the same time? That doesn't make sense to me.Thanks for your input.
  • #1
halli
13
0
Can you help me out and tell me if I am right or wrong when I say the following:

Think of a free fall.

As we see something in a free fall here on Earth we are really seeing/experiencing it in 2d not 3d. An object that moves in a straight line from one point to another is traveling/falling in 2d. Space/distance is increasing all the time between the object falling and its starting point.

An object that falls in 3d must be falling “in”, or “out”. If something falls “in” it falls into one point from all directions. Space/distance is increasing from all directions. If something falls “out” it is falling outwards from one point in all directions, space/distance is increasing from one point and out.

Please comment

Best regards

Halli
 
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  • #2
halli said:
Can you help me out and tell me if I am right or wrong when I say the following:

Think of a free fall.

As we see something in a free fall here on Earth we are really seeing/experiencing it in 2d not 3d. An object that moves in a straight line from one point to another is traveling/falling in 2d. Space/distance is increasing all the time between the object falling and its starting point.

An object that falls in 3d must be falling “in”, or “out”. If something falls “in” it falls into one point from all directions. Space/distance is increasing from all directions. If something falls “out” it is falling outwards from one point in all directions, space/distance is increasing from one point and out.

Please comment

Best regards

Halli

What's your point? Is there a question in here somewhere? What is giving you trouble?
 
  • #3
Thanks for the reply phinds

My trouble is that I have come to the conclusion that an object that falls straight down is falling two dimensionally, even though it is in a three dimensional world. It travels from point A straight to point B (no wind, resistance,....)

If that conclusion is right then an object that would fall three dimensionally must be falling from all angles/directions. Might compare it to an inflated balloon that is losing air. Its surface is falling into the centre.

This is quite important.

Does anyone agree or disagree with this conclusion? Is there something that has already been written about this? Or am I just a very troubled person :)

Please comment

Best regards
halli
 
  • #4
halli said:
As we see something in a free fall here on Earth we are really seeing/experiencing it in 2d not 3d. An object that moves in a straight line from one point to another is traveling/falling in 2d.
You can describe straight line motion as 1-dimensional, if you like.
Space/distance is increasing all the time between the object falling and its starting point.
OK.
An object that falls in 3d must be falling “in”, or “out”. If something falls “in” it falls into one point from all directions. Space/distance is increasing from all directions. If something falls “out” it is falling outwards from one point in all directions, space/distance is increasing from one point and out.
I cannot make sense of these words.
 
  • #5
Thanks Doc Al

See post 2 for ?better? explanation.
 
  • #6
halli said:
See post 2 for ?better? explanation.
I assume you mean post #3. Sorry, that's equally obscure. I don't see what you mean by "an object that would fall three dimensionally must be falling from all angles/directions". Why in the world would you think that?
 
  • #7
Thanks again Doc Al

Why? Not easy to answer.

The first question maybe should have been:

Do you think it is possible for objects to "fall" three dimensionally (at least in theory)?

But I needed to try to explain it somehow.

So is it obscure or maybe a possibility in your opinion?
 
  • #8
halli said:
Do you think it is possible for objects to "fall" three dimensionally (at least in theory)?
I have no idea what you mean by 'falling three dimensionally'.
 
  • #9
Thanks Doc Al, I appreciate it

I will try one more time with a statement:

A balloon that is collapsing is “falling” 3 dimentionally.

Could this be true in your opinion?

Thanks again
Best regards
halli
 
  • #10
halli said:
Thanks Doc Al, I appreciate it

I will try one more time with a statement:

A balloon that is collapsing is “falling” 3 dimentionally.

Could this be true in your opinion?

Thanks again
Best regards
halli

All I can make of any of this is that you are playing with words and confusing yourself. Collapsing is a perfectly valid description of what the balloon is doing and I guess if you like to think of that as "falling" in 3D you can but I don't get what that means.

A steel ball that drops from the upper atmosphere to Earth is falling in 3D due to wind shear and I seriously doubt that you could describe such an actual trajectory in less than 3D. An IDEAL situation could have something moving only in 1D as it falls.

What is your basic problem here? What is it that you are trying to figure out? Playing with words isn't getting us anywhere.
 
  • #11
Hei guys

You might say I am playing with words, that is right.

But I am trying to understand some very basic forces. I am trying to understand them logically but not mathematically. And with that I have only words. The definition of things with words is sometimes confusing. Using one word instead of another can change everything because of our different understanding of different words.

I am sorry if it seems like I was wasting your time, but the last answer really helped me and my weird head :)

Thanks again
Best regards
Halli
 
  • #12
As has been said, you can think of simple falling as being in only one dimension, as the object is only experiencing the force of gravity, and it falls in a straight line (down). If we add another force that causes the object to veer left or right while falling (wind, or being shot out of a gun) well then we'll need to talk about it in two dimensions.

If we add yet another force that's not in the same plane as gravity and the second force, then that object will fall down, left/ right, and in/out. Indeed, we'll need to discuss the object in all three dimensions in order to desrcibe its motion. A deflating balloon will spin around and forces will be imparted on it in all directions, so we'll need to use all 3 dimensions to descibe its trajectory.

Realistically, to descibe the motion of ANY object, we need to know what it's doing in all three dimensions. However, the wording of a problem usually tells you about these other dimensions. For example, if someone drops a bowling ball from the 3rd floor, you know that it's side-side velocity is close to 0 due to the word "drops"...and hence we can ignore that dimension. You can also assume that there will be no other significant force due to the omission of words such as "explosion", "tornado", or "airplane" and hence using this information, we can simplify an otherwise 3d problem into 1d.
 
  • #13
Thank You L sos

What I am trying to imagine is not exactly a balloon loosing air from one point and there for spinning around.

It is more of a scenario of theoretical situation where I am trying to imagine this:

A steel ball is positioned in vacuum. Space is "growing" or "increasing" all around it.
Will that steel ball experience forces of collapse into its center of mass?

Might be a stupid example to call it a "free fall in 3d" but that is how I have been trying to understand it.

Best regards

halli
 
  • #14
halli said:
A steel ball is positioned in vacuum.
OK.
Space is "growing" or "increasing" all around it.
What do you mean?
Will that steel ball experience forces of collapse into its center of mass?
Forces due to what?
 
  • #15
halli said:
Thank You L sos

What I am trying to imagine is not exactly a balloon loosing air from one point and there for spinning around.

It is more of a scenario of theoretical situation where I am trying to imagine this:

A steel ball is positioned in vacuum. Space is "growing" or "increasing" all around it.
Will that steel ball experience forces of collapse into its center of mass?

Might be a stupid example to call it a "free fall in 3d" but that is how I have been trying to understand it.

Best regards

halli

Seems like we've gone from object in free fall to objects undergoing gravitational collapse. You likely would have gotten a more coherent and helpful answer if you had asked the question you were trying to answer instead of asking a different question.

Doc Al is gently trying to nudge you into thinking about what you are saying. You should read up a bit on the expansion of the universe and its effect (lack of effect, actually) on gravitationally bound systems.

It's clear from your question that you don't understand that and I think you'd find it interesting.
 
  • #16
Halli, you could easily describe any objects motion as 1d. Where 3d comes into it is that it is free to change its vector of motion in 3 different directions. If I swing a bucket on a rope around my head you could say that at each infinitesimally point in time the bucket is only traveling in one direction, and that at the next infinitesimally point in time forward the direction it is traveling has changed but that it is still traveling in one direction.

In your balloon example, each particle in the balloon is traveling in one direction that may change over time, yet overall that direction is towards the center of the balloon if it is collapsing.
 
  • #17
I think what he's grappling with is that, to describe an object falling in a straight line only requires one dimension of change. In the other two dimensions, coordinates do not necessarily change. (Though it is simply a question of what coordinate system you use. You could use an coordinate system that's oblique to the direction fall such that it tracks the object changing its coordinates across all three dimensions.)

He's asking if it is possible to have an object fall in such a way that it requires coordinate changes in all three dimensions.

Well, you can get two at least, by having the object fall in an arc. To track it requires a coordinate system adjustment to align at least one dimension, but you cannot describe the arc without tracking change in a minimum of two dimensions.

Can anyone describe a circumstance in which a minimum of three coordinates are required to describe an object falling?
 
  • #18
DaveC426913 said:
Can anyone describe a circumstance in which a minimum of three coordinates are required to describe an object falling?

Some sort of helix type motion in the fall, like a wiffle ball?
 
  • #19
Drakkith said:
Some sort of helix type motion in the fall, like a wiffle ball?

Yeah. The trouble is, you end up invoking external forces other than free falling (i.e. gravitational attraction).
 
  • #20
I think you understand what I mean now. Thanks for the patience. I do not know all the right words to use.

But I knew before I asked I could not mention GRA... and I am not going to. I will be banned if I do.

I read what I could find on the expansion of the universe and its effect (lack of effect, actually) on gravitationally bound systems. What I found did not help me. Could you give me some links to a good article or similar to this matter?

But still I think about my ball. Made of whatever. All alone in space. And space is growing/increasing from all directions/all around. Do any forces „appear“ in the mass center of the ball?

I have been bouncing from yes, no, yes, no, yes, no, yes, no. This damn ball has given me allot of headache. And it doesn’t even exist.

But I really think (theoretically of course) it would get affected by the space increasing around it and seek for falling into its own mass center.

But I am not 100% sure because if that would happen to the ball in my head allot of things could be answered.

I am not surrounded by people I can discuss this hobby of mine with. So I searched for someone like you guys and girls to ask. And I want to repeat that I am not making any statements. I realize that I might be wrong. And I know that I know a lot less then you guys and girls about physics.

Thanks and best regards

halli
 
  • #21
halli said:
But I knew before I asked I could not mention GRA... and I am not going to. I will be banned if I do.

What is GRA?

I read what I could find on the expansion of the universe and its effect (lack of effect, actually) on gravitationally bound systems. What I found did not help me. Could you give me some links to a good article or similar to this matter?

Try the search function here on PF. There should be plenty of threads about it.

But still I think about my ball. Made of whatever. All alone in space. And space is growing/increasing from all directions/all around. Do any forces „appear“ in the mass center of the ball?

No forces appear. Also, in my understanding at least, near a source of gravity space stops expanding, hence why we can't see expansion until we get to the scale of intergalactic space.

But I really think (theoretically of course) it would get affected by the space increasing around it and seek for falling into its own mass center.

Another view is that the expansion is happening everywhere, but the fundamental forces of nature hold everything together still. So for your ball the electromagnetic force, strong force, and gravity easily overcome any expansion. It might be infinitesimally larger in size due to expansion, but that's it. This does NOT count as "falling into it's own mass center" as gravity is by far the weakest of the 4 forces of nature and none of the particles making up the ball are actually moving inward, so they can't count as falling. It is the electromagnetic force and the strong force holding matter together at this scale. Once you get to large objects such as planetoids and above gravity starts to take over as the dominate force holding everything together.
 
  • #22
I just had a thought halli ... probably wrong but it COULD explain your misconception. Is it perhaps that you are seeing in your minds eye a volumn of space with the ball in it and then you see that space expanding but somehow you are thinking of it as occupying the same size in your mind, which then makes the ball seem to shrink because it IS occupying less and less of the space.

This seems so obviously wrong that I'm just about sure it can't be your thought process, but I thought I'd mention it.
 
  • #23
Hei

I see what you mean phinds, but that is not the case. The space has no size, if it had it then the only thing that matters is that it is "larger" after each "moment" (not the best way to say it but I think you know what I mean).
So the "size" of space is not important, just that it is "expanding"/"growing"/"increasing" but my ball never changes its size.

And Drakkith thank you for your comment. I have so little time right now that I will have to go through it tomorrow. I am little bit behind you guys in speed, I have to have time to focus on each "case". But I am looking forward to go through it.

Thanks again and best regards

halli
 

Related to Answer: Basic Physics Question - Free Fall in 2D or 3D?

1. What is free fall in 2D or 3D?

Free fall refers to the motion of an object under the influence of gravity only. In 2D, the object will only have motion in the x and y directions, while in 3D, it will also have motion in the z direction.

2. What is the formula for calculating free fall in 2D or 3D?

The formula for calculating free fall in 2D or 3D is d = 1/2gt^2, where d is the distance traveled, g is the acceleration due to gravity, and t is the time.

3. How does air resistance affect free fall in 2D or 3D?

Air resistance can have a significant effect on free fall in 2D or 3D. As objects fall, they encounter air resistance which opposes their motion and can cause them to reach a terminal velocity, where the force of air resistance is equal to the force of gravity.

4. What is the difference between free fall in 2D and 3D?

The main difference between free fall in 2D and 3D is the number of dimensions in which the object is falling. In 2D, the object will only have motion in the x and y directions, while in 3D, it will also have motion in the z direction.

5. How is free fall in 2D or 3D used in real life?

Free fall in 2D or 3D is used in many real-life scenarios, such as skydiving, bungee jumping, and projectile motion in sports like basketball and baseball. It is also used in physics experiments to study the effects of gravity on objects.

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