# Why do you feel heavier in water?

potto
TL;DR Summary
I am searching for the common explanation why people believe it is so. Google and other places are suggesting that it related to gravity. However. the gravity (buoyancy) reduces our weight. The question: do we really heavier in water? If it is not the case, what makes us think that we are heavier? Is it a physical phenomenon that it actually demand additional force?

Gold Member
I do not think that people “feel heavier” in the water; however, water is thicker than air so drag forces are larger.

russ_watters, topsquark, Lnewqban and 1 other person
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The question: do we really heavier in water? If it is not the case, what makes us think that we are heavier? Is it a physical phenomenon that it actually demand additional force?
There must be a name for this where cause and effect are somewhat scrambled in the brain, in this case the feeling and conclusion that being immersed in water makes you ' heavier'.
I have even felt it not so much as when coming out of a bath, but fully noticable when raising an arm out of the water when lying in the bath. The arm really does feel as if it has become way much heavier.

It is a phycological mind trick.

Bear in mind that bouyancy is a wonderful thing. Astronauts train under water in their space walk suits giving them the impression towards weightlessness. Except for the difference of viscosity of actual space ( which is it doesn't have any ) to that of water, the experience would be as if the astronaut is 'floating' in space. The forces that his/hers limbs would have to overcome for movement would be that of the flexing of the suit and moving the limb, or body, through a viscous fluid ( the water ). Since the gravitational attraction of the astronaut towards the centre of the earth is compensated by their bouyancy, I would imagine that the experience is somewhat akin to doing a spacewalk along side their craft in freefall orbit around the earth.

How could you, or anyone else, come to the conclusion that being in the water makes you heavier?
Normally, out of the water, when we move our body, or any part of it such as limbs, we are accustomed to having to exert a certain force, and think not to much about it.
When in the water, we can move our bodies, and our limbs, and not think to much about it also, as long as the movements are not to drastic.
That is until when when we try to run forward, or much an extended arm quickly in an arc, as two examples. In these instances, we quickly do realize the there is the water all around us, and being the thinking creatures that we are, the density and viscosity of the water must play a part in hindering the velocities and accelerations that we are so accustomed to when immersed in air ( ie where we normally live our lives ).

But try to lift an arm slowly ( probably not as noticeable if movements are quickly done ) out of the water. Or try to lift your whole self out of the swimming pool. The feeling does come about that the arm, or your body, has somehow become heavier when it leaves the water.
Your brain using its own logic does come to the erroneous conclusion that we have grown heavier. We don't have a bouyancy centre within the brain that tells us " OK, extra muscle force needed, arm is coming out of the water ". The extra force is the difference of the bouyant arm ( not much force to move upwards ) to that of weight of the arm in air ( a greater force ) . Since this happens say in less than a second ( a step function if you are into systems control ) we do think about it - ie we have to exert more muscle contraction to lift the arm higher from the water into the air. The brain, from somewhere deep within its 'erroneous centre' scrambles for a cause, and concludes that the arm has become heavier.

PS. Besides astronaut training , some physiological therapies do involve exercises while being immersed within water.

potto, topsquark and Lnewqban
potto
There must be a name for this where cause and effect are somewhat scrambled in the brain, in this case the feeling and conclusion that being immersed in water makes you ' heavier'.
I have even felt it not so much as when coming out of a bath, but fully noticable when raising an arm out of the water when lying in the bath. The arm really does feel as if it has become way much heavier.

It is a phycological mind trick.

Bear in mind that bouyancy is a wonderful thing. Astronauts train under water in their space walk suits giving them the impression towards weightlessness. Except for the difference of viscosity of actual space ( which is it doesn't have any ) to that of water, the experience would be as if the astronaut is 'floating' in space. The forces that his/hers limbs would have to overcome for movement would be that of the flexing of the suit and moving the limb, or body, through a viscous fluid ( the water ). Since the gravitational attraction of the astronaut towards the centre of the earth is compensated by their bouyancy, I would imagine that the experience is somewhat akin to doing a spacewalk along side their craft in freefall orbit around the earth.

How could you, or anyone else, come to the conclusion that being in the water makes you heavier?
Normally, out of the water, when we move our body, or any part of it such as limbs, we are accustomed to having to exert a certain force, and think not to much about it.
When in the water, we can move our bodies, and our limbs, and not think to much about it also, as long as the movements are not to drastic.
That is until when when we try to run forward, or much an extended arm quickly in an arc, as two examples. In these instances, we quickly do realize the there is the water all around us, and being the thinking creatures that we are, the density and viscosity of the water must play a part in hindering the velocities and accelerations that we are so accustomed to when immersed in air ( ie where we normally live our lives ).

But try to lift an arm slowly ( probably not as noticeable if movements are quickly done ) out of the water. Or try to lift your whole self out of the swimming pool. The feeling does come about that the arm, or your body, has somehow become heavier when it leaves the water.
Your brain using its own logic does come to the erroneous conclusion that we have grown heavier. We don't have a bouyancy centre within the brain that tells us " OK, extra muscle force needed, arm is coming out of the water ". The extra force is the difference of the bouyant arm ( not much force to move upwards ) to that of weight of the arm in air ( a greater force ) . Since this happens say in less than a second ( a step function if you are into systems control ) we do think about it - ie we have to exert more muscle contraction to lift the arm higher from the water into the air. The brain, from somewhere deep within its 'erroneous centre' scrambles for a cause, and concludes that the arm has become heavier.

PS. Besides astronaut training , some physiological therapies do involve exercises while being immersed within water.
I think that you have a point. This question bother me so I have research the web and I think that I found the solution. This phenomenon is physical and it based on the idea that when the air or water you move additional mass that move because you occupy volume. I found this explanation on
https://zenodo.org/record/6800537#.Y959u8bMI-3 chapter 13 p. 467 in a free book on "Basics of Fluid Mechanics" . Think about a body in a box full of fluid. if the body moves some of the liquid move allow the body to get the new place while some fluid will take the proce that the body was before. It the body accelarate then the liquid will accelerate as well. The liquid movemnet is the additional mass that makes us feel heavy.

256bits
Gold Member
I found this explanation
The added mass explanation does exist as a body moving through a fluid displaces the fluid which has to move in the opposite direction.
But, with our bodies, which are mostly water, the bouyancy effect cancels out the added mass effect.
The body would have then an effective mass pretty much the same as that in air.

I like my explanation, with some bias :)
I do not feel heavy in the water. I feel restricted.
Only when getting out at the edge of a pool, or slowly raising an arm out of the water do I feel heavier.
Perhaps some others feel it differently.

hutchphd, Merlin3189 and Lnewqban
potto
But, with our bodies, which are mostly water, the bouyancy effect cancels out the added mass effect.
The body would have then an effective mass pretty much the same as that in air.''

How the buoyancy cancel the added mass? It is not clear to me. According the book Basics of Fluid Mechanics''
the added mass can occur in any direction if the buoyancy is vertical and the added mass is horizontal how they cancel each other? I think that force is a vector. Maybe?

Let me explain in the poor man words (I think that the book explains it better than me) . Take a body in a close box with no exist to the fluid that is inside. If you tie a very thin wire to the body and pull the body will move. If we assume that he liquid has no viscosity then body will push some fluid and some fluid will move to replace the space that previously occupy by the body. If the body is accelerating the liquid is also accelerating. This acceleration of the fluid is the source of the added mass. According to the book some claim that it is a matrix of 6x6 some thing that I do not understand. Be it as it may, the fact that the body has move fluid is clear and in the water the added mass is several times the size of the our body. That what make it difficult to run in the water.

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FWIW I don't feel heavier in water. I can float in water, but I don't even consider attempting that in air!

In air, I feel weight pulling me down. In water the new forces I experience seem to push sideways when I try to move. That is not weight. Nor even mass, since moving at steady speed requires continuing effort, not just to accelerate it.

Either your experience is different from mine, or you have described it differently. Finding explanations depends on clear specification of the issue.

256bits and Lord Jestocost
potto
FWIW I don't feel heavier in water. I can float in water, but I don't even consider attempting that in air!

In air, I feel weight pulling me down. In water the new forces I experience seem to push sideways when I try to move. That is not weight. Nor even mass, since moving at steady speed requires continuing effort, not just to accelerate it.

Either your experience is different from mine, or you have described it differently. Finding explanations depends on clear specification of the issue.
Thank you for your reply. There are two phenomena that occur in the same time. One that you are talking about which buoyancy. Your weight in the water is smaller then in air. People conflating this effect with fact that move a hand for example you fill that is very hard to do and it harder several times as compared to move the hand in air. The common expiation is there is viscosity. However the sheer amount of force made smart people to realize that there something else. I read in Basics of fluid mechanics'' https://zenodo.org/record/6800537#.Y97u18bMI-3 the right explanation. This effect is called the added mass which was in investigate by the way a British man known as Charles Darwin. I also found in a poor man explanation in wiki on added mass. While I am not expert but what I gather from the book I seems to me that the movement of the body creates movement of the fluid. This movement of liquid is the added mass to the body. It has nothing to do with viscosity. While the viscosity might appear in the calculations it is insignificant as compared to the added mass effect. I am not eloquent as the book, it seems to be correct my observation when you move your hand in the water it is require larger forces.

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Agree viscosity probably negligible. I just think the extra mass you feel is the mass of the water you have to move to get through it. Perhaps the viscosity people say that the water flows round your limbs and you feel only the viscous drag. My feeling is that I am pushing the water away from me, some may flow around, but most moves off in turbulent swirls dissipating energy (bulk KE to thermal KE), so I do a lot of work which shows up as large force opposing my movement. You can call this an "added mass effect" though I'd not heard that term before. It doesn't add to my momentum, so it's more like friction, always opposing movement, but not limited in magnitude, and related to speed. If I do a racing dive (pretty much illegal in UK pools these days!) I try to "streamline" my body to move as little water and create as little turbulence as possible: maybe then viscosity is significant a factor? Maybe the drag your hair causes is viscous, but swimmers seem to think it worth shaving or wearing caps to reduce it.

Buoyancy to my thought, is a separate force from gravitational weight, but I agree you experience it as a net change in weight. So I should perhaps have taken that meaning. But that means we don't feel heavier in water, rather lighter.

Lnewqban
Gold Member
According to the book some claim that it is a matrix of 6x6 some thing that I do not understand
Degrees of freedom for a body moving in 3D space - in a direction of the 3 axis, and rotation about the axis.
the movement of the body creates movement of the fluid. This movement of liquid is the added mass to the body. It has nothing to do with viscosity. While the viscosity might appear in the calculations it is insignificant as compared to the added mass effect.
The part missed is the acceleration/deceleration of the body surrounded by fluid in some manner.
In fluid mechanics, added mass or virtual mass is the inertia added to a system because an accelerating or decelerating body must move (or deflect) some volume of surrounding fluid as it moves through it

the added mass can occur in any direction if the buoyancy is vertical and the added mass is horizontal how they cancel each other? I think that force is a vector.
That what make it difficult to run in the water.
Excellent point.

It should then be easier to pull/push a bouyant body in the vertical direction rather than the horizontal, which could be the case. One could devise an experiment for investigation.
At steady state velocity, the force necessary should be the same, where drag effects will predominate towards keeping the body at constant velocity I believe.

While the viscosity might appear in the calculations it is insignificant
Since drag is a function of velocity through the fluid, the added mass inertia effect could overhelm with changes in velocity, since it is immediate, while the change in drag is a delayed effect. I don't think the 'insignificant' description is applicable under all situations. With velocity =0 , the drag contribution of the force upon commencement of acceleration is zero. At other velocities, is the work needed due to the added mass effect always greater than the work needed due to the drag? Other than doing some calculations to verify, the statement to me becomes suspect at higher velocities.

russ_watters and potto
Gold Member
it seems to be correct my observation when you move your hand in the water it is require larger forces.
You are changing your original question. It feels like you are pushing on something, not that your hand feels heavier.

russ_watters
potto
Degrees of freedom for a body moving in 3D space - in a direction of the 3 axis, and rotation about the axis.

The part missed is the acceleration/deceleration of the body surrounded by fluid in some manner.
In fluid mechanics, added mass or virtual mass is the inertia added to a system because an accelerating or decelerating body must move (or deflect) some volume of surrounding fluid as it moves through it

Excellent point.

It should then be easier to pull/push a bouyant body in the vertical direction rather than the horizontal, which could be the case. One could devise an experiment for investigation.
At steady state velocity, the force necessary should be the same, where drag effects will predominate towards keeping the body at constant velocity I believe.

Since drag is a function of velocity through the fluid, the added mass inertia effect could overhelm with changes in velocity, since it is immediate, while the change in drag is a delayed effect. I don't think the 'insignificant' description is applicable under all situations. With velocity =0 , the drag contribution of the force upon commencement of acceleration is zero. At other velocities, is the work needed due to the added mass effect always greater than the work needed due to the drag? Other than doing some calculations to verify, the statement to me becomes suspect at higher velocities.
Very good point, drag is related to velocity. I cannot agree more with this statement. And this point actually strengthen the argument for the added mass. Take this illustration, suppose you have zero velocity hence you have zero drag (viscosity effect). In the same time you have large "force" objecting to your acceleration. This large force is the added mass. The description of water (liquid) movement can be summarized or characterized by the fact that no vacuum is created. I believe that you will agree with that. Thus when the hand or the body moves in the water it push some in front of it and the same time some water has to replace the previous space the where the hand (body) was before. The path the water has to go though determine how much mass has moved. This mass depends on the shape of the hand (body) and the boundaries of the container. Hence hairy hand or wide body have larger added mass while thin bodies have smaller added mass.

potto
I take the point that was made by others below. The viscous forces related to the velocity. If the velocity is zero than there is no viscous forces. Yet the resisting force is very large which can be explain only the added mass.

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Th technical term required here is kinesthetics. The perception of static weight of body parts is driven by muscle tone. If our arm is out of the water our brain percieves it to be heavier than the remaining floating body.

russ_watters
potto
Th technical term required here is kinesthetics. The perception of static weight of body parts is driven by muscle tone. If our arm is out of the water our brain percieves it to be heavier than the remaining floating body.
It is true that our body (brain) make us think in a certain ways. The question is whether there is a physical effect that actually we feel. I think that there is a strong effect which is the added mass. This effect happend is because we have to move the liquid around us (or accelerate it).

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But this concept (I will guess) tacitly assumes a spherical arm of unchanging shape. I do not believe it will be perceived as mass by a sentient human.

256bits
potto
I read your link. I would sugget some changes to the text in the page if you would be interested. The accuracy of the page can be increased.

Frabjous
potto
But this concept (I will guess) tacitly assumes a spherical arm of unchanging shape. I do not believe it will be perceived as mass by a sentient human.
That is the exact point I m trying to make. It not have to be circular. Any physical shape will be good. Image square body pushing the water. The water in front is pushed but in turn push the water a head of it. This continue until some water take the place of the body where it was before. The path determines the mount of water praticipate the body movement. This effect is called added mass which depends on the body and shape of the box.

Gold Member
Hence hairy hand or wide body have larger added mass while thin bodies have smaller added mass.
Yes. It does depend upon the shape of the object.

The actual question as I understood, is whether people 'feel' heavier in the water.
Maybe some do, and maybe some don't.
You seem belabored on the added mass, which is a thing in its own right, for solving some problems.
No argument there for solving some problems.

But can it be 'THE' explanation for a human 'feeling' of being heavy in water, which by the way has not been verified except that from the opening heading and initial post as being common, and may or may not exist, . Do you know of, or can you find any study of the kind?
The discussion does need some actual beef to mull over so as to continue as a topic.

russ_watters
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This effect is called added mass
You do understand this is not "mass" that has any direct gravitational consequence?

potto
You do understand this is not mass that has any gravitational consequence?
I would not agree with you. Mass in physics and engineering is defined as
the resistance to the acceleration (not to gravity specifically). And it happend that the added mass is affected by the gravity (put water on scale and you have a weight). In this case, this added mass resisting the acceleration of the body. The body does not feel this mass when it is at rest. In fact today, \textbf{all} the calcuations of ship movement calculate the added mass which some cases more than the ship weight.

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Frabjous
potto
Yes. It does depend upon the shape of the object.

The actual question as I understood, is whether people 'feel' heavier in the water.
Maybe some do, and maybe some don't.
You seem belabored on the added mass, which is a thing in its own right, for solving some problems.
No argument there for solving some problems.

But can it be 'THE' explanation for a human 'feeling' of being heavy in water, which by the way has not been verified except that from the opening heading and initial post as being common, and may or may not exist, . Do you know of, or can you find any study of the kind?
The discussion does need some actual beef to mull over so as to continue as a topic.
Yes, there large body of research on this point, I can refer you to some papers. this kind of work refers as fish locomotion. Or swimming bodies studys. It is well established that the added mass must be considered.

Gold Member
According to the book some claim that it is a matrix of 6x6 some thing that I do not understand.
Yesterday, you didn’t understand this.
Yes, there large body of research on this point, I can refer you to some papers.
Today, you are recommending research papers.

I am leaving this thread now.

russ_watters
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. It is well established that the added mass must be considered

This requires several references please. I do not understand your point. The concept of "dressed" mass only goes so far.

256bits and russ_watters
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... This movement of liquid is the added mass to the body. It has nothing to do with viscosity. While the viscosity might appear in the calculations it is insignificant as compared to the added mass effect. I am not eloquent as the book, it seems to be correct my observation when you move your hand in the water it is require larger forces.
Because its fixed volume, a brick submerged in water displaces a unique mass of water, being moving or not.
When forced to move along a horizontal line, it offers different resistance (or drag) depending on the position in which it is forced to move.

How can that be if, according to the added mass idea, when the brick is forced to move through the water, it pushes exactly the same mass of water in front of it than the mass of water that has to fill the space where the brick was before.

Regardless the path the water has to flow through, the same mass of it has been forced to moved.
This mass depends solely on the volume of the brick times density of water.

Could we conclude then that the resistance to movement (or drag) depends on the shape in which the submerged object faces the movement?

Merlin3189
potto
 Because its fixed volume, a brick submerged in water displaces a unique mass of water, being moving or not. When forced to move along a horizontal line, it offers different resistance (or drag) depending on the position in which it is forced to move. 
The first statement is correct and I agree with it. The second part is not correct. The direction of the movement is irrelevant to the drag (only the oreintation of the body) . However, the gravity has effect on the forces (or the acceleration).

 How can that be if, according to the added mass idea, when the brick is forced to move through the water, it pushes exactly the same mass of water in front of it than the mass of water that has to fill the space where the brick was before 
This concept is called mass conservation. The pushed fluid push other fluid ending by filling the last place. You can think about as a chain (it is not really) as this description make it easier to visualize the phenomenon.

 Regardless the path the water has to flow through, the same mass of it has been forced to moved. This mass depends solely on the volume of the brick times density of water. 
Not exactly correct. The amount of water that has to flow depends on the shape of body and the boundaries (shape) of the box.
Thus, thus mass depends on the volume of the body, shape of the body and density of the block (and orientation). I saw in the book a table describing the different shapes with different coefficients. I think that he got the information from other references like this one (see in the references in the book)
People have to find value of the added properties from experiential work. For example, (Aso, Kan, Doki, and Mori 1991; Brennen 1982; Molin, Remy, and Rippol 2007)

 Could we conclude then that the resistance to movement (or drag) depends on the shape in which the submerged object faces the movement?