Why Do Things Float?
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- čas přidán 19. 06. 2024
- Ever wonder why things float? Buoyancy arises from the weight of a displaced fluid, a phenomenon described by Archimedes principle.
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COOL LINKS & SOURCES
Densities of Solids:
www.engineeringtoolbox.com/den...
Density of Water:
www2.volstate.edu/CHEM/Density...
hypertextbook.com/facts/2007/A...
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CHAPTERS
00:00 Introduction
00:09 No, it's not density.
01:44 Experiment Time!
02:30 Weight
03:03 Pressure
03:30 Origin of Buoyant Force
03:50 Archimedes Principle
04:22 Outro
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Corrections:
04:09 Bowling balls less than 12 pounds (5.44 kg) will float. Bowling balls greater than 12 pounds (5.44 kg) will sink.
Nick Lucid's first video of science asylum. Nostalgic. Really Enjoyed it. 🤣
This really takes me back... in an extremely cringy sort of way.
(Also, it's not my first video. It's just my earliest _public_ video. My first 20ish videos are set to private. Yes, they're that bad.)
@@ScienceAsylum could you set them to public for historical reasons?
If the duck were solid, that would be true. However, the duck is hollow. Since there's air inside, the rubber doesn't fill all the same volume that the water does. It lets the duck take up more space without being any heavier. Boats (like metal fishing boats) float for the same reason. The density rule really only works for liquids or completely solid objects, so it's a bit limited.
4:18 "Things float because of weight". Well, of course not only because of weight, but also because of volume and fight for supremacy. Just to respect both parameters using "density" is just a useful simplification.
Dear, you are cheating... if the ninja duck is hollow you are artificially changing the density of the objet put in the water. I call density the following: weight/volume
No matter which substances are involved. With this in mind, floating is only a matter of density. Period.
@@francescoruggiero4974 but you don't mix the density of an object with what's inside of it. however, when you do consider all the mass on the object when measuring weight. See the difference? How can you measure the density of a human body with all its elements? well, you can't. But it's easy to measure the total weight.
Nick is exactly right, this is the best video on why things float I have found. I am a middle school level science teacher and make Cartesian Divers with my students. Getting the science right for the kids is very important to me. For many years I have been so confused about using density to explain floating and sinking, generations of kids were confused by what their teachers taught them, myself included. The cool thing is, the confusion can be eliminated by not even mentioning density and focusing on what is really happening, it's so much easier to understand that way.
The density rule adds so much confusion because the volume of an object is not necessarily the same as the volume of fluid displaced by the object. There is also the problem of how you define the density of an object. Take for example a cup, do you include the air inside the cup or do you not ? Some people might say yes and we call it average density, the mass of the cup and air divided by the volume of the cup and air in it. If you work it out its well under the density of water so the cup should float. However when you submerge the cup in water the right way up it fills with water and sinks. Others might say the density of the cup does not include the air inside, its just the mass of the cup material divided by the volume of that material (eg plastic or glass). If you work it out it is greater than the density of water so it should sink. But if you lower a cup into the water upside down the air is trapped underneath and starts to displace water and it floats. So are we saying the density of the cup depends on which way up it is ! lol So much confusion, why do we do this, its so much better and easier to just ask how much water is being displaced and what is the weight of the object. Every kid always asks how does an ocean liner float when its made of thousands of tons of steel ? You are just going to confuse them by saying well there is air below the water line inside the ship which if you include as part of the volume of the ship makes the density of the ship less than water. You are missing out on explaining that its the displacement of a huge amount of water by the ships hull that creates a very large buoyancy force that balances the very large weight of the ship.
Density can be used to predict the floating or sinking of uniform objects submerged in a fluid but its only a special case. I would only talk about it with advanced students who fully understand the science behind why things float and sink. They should know buoyancy is caused by gravity which causes pressure variation with height in a fluid. If gravity switched off there would be no buoyancy. Fluid pressure increases as you go towards the centre of mass of the Earth so there is a net upward force on an object. Archimedes discovered this net upward force is equal to the weight of the fluid displaced. As Nick said, its a battle between this upward buoyancy force and the downward weight force on the object. You should not use density to explain why things float and sink because it is not the fundamental cause of it, it can only be used as a tool in special cases to make predictions, but never bring it up when explaining it to a kid. Also we tend to forget that every object has a buoyancy force on it due to being in the air, its just much smaller than in water. Any fluid will create a buoyancy force.
Hello!
I read what you said and I agree, but I don't understand one thing about the video and about what you said. If you can, please help me.
The duck in the video is suposed to be an uniform object, right? So, how can it float if it's denser than water?
As you wrote, "Density can be used to predict the floating or sinking of uniform objects submerged in a fluid but its only a special case."
I agree competely, but my point is that the duck is uniform, so, why doesn't it sink?
Thank you very much. I'm from Portugal, so sorry for any English mistake.
How would you explain oil floating on water without mentioning density? For a well defined object it may be ok to disregard density from the explanation, but not always.
@@jlpsinde It's not uniform (assuming I'm correctly understanding you're use of the term. It has air in the middle of it.)
Is that a rubber udcky with AIR inside? if it has ther air inside then the density is less than water and you cannot just measure the density of the ruber part. If it is a solid duck with density more than water I'd be really surprised and I want to see proof.
@@Will-be-free interesting!
The reason the toy duck floats is because its average density is less than water. Although you may be right that the density of pure soft rubber is greater than that of water, the duck has air in it, and the NET mass / volume is, in fact, less than that of water.
Density does, actually, have a direct relationship with floating.
It is true that you can think of it in terms of buoyant force vs gravitational force, but if you rearrange the equations and insert the variables involved, you will see that it is impossible for an object to float if its average density is greater than water, and vice versa.
"Average density" makes sense only when you're referring to a uniform mix of different elements/materials (like metal alloys), at least to me anyway. What you're really referring to is the pressure applied by the rubber duck's weight on the water surface. The surface area of the bottom of the rubber duck is distributing the rubber duck's weight over a wider area than if the rubber duck was nothing but a clump of rubber.
All the air in the rubber duck does is keep the rubber duck from collapsing under the pressure of the atmosphere (not density because the atmosphere is applying forces to the surface of the rubber duck), which is why the rubber duck maintains its bottom surface area and therefore floats on water.
That's my understanding, anyway.
no, its because all the kids sing the rubber ducky song so no matter what a rubber ducky will never sink. It's called perception, if you think you can fly and trick everyone to believe you. I know you can fly. I've seen it before... lmfao..
wth, are yall talking about, do you have a video I can look at over and over to figure this shit out. I want to fucking fly already. lmfao..
Water density is actually density at molecular level.
nerds
we all float down here
You'll float too!
Boats can be made of concrete, or steel which are both denser than water. Some barges are made of concrete, most carriers have a huge amount of steel. If the boat displaces an amount of water which weighs more than the dry ship, it floats. Bonus points if the boat has a lot of its weight near the bottom of the boat so it is stable in the water...
The weight of the ship is mostly made up of air though. The steel-air mix that makes up the boat is lighter (less dense) than water. If you filled the ship with heavier air, it would sink. I really don't see how the density argument is wrong at all.
The only way it can displace more weight in water than itself is if the boat is full of AIR and thus the average density is indeed less than the water.
btw, that ‘stability’ is called a ‘righting moment’ in naval engineering terms
@@SpaghettiToaster The real problem is that 'density' has different meanings depending on the context. If i make a simple concave shape and i ask a scientist to tell me what is its density he won't average any air. He only will average the air if i tell him that i made that shape with the intention of being able to float in water.
This second 'density' varies depending on future intended human purposes, while the first 'density', the scientific concept, is just a fixed property of an object.
Maybe if we had two different words ('density' and 'floating density', idk) this whole argument would be much more clear.
@@emanuelscalvin I know. The problem is that sometimes you need to take into account the air and sometimes not. For example, we have two boats. Same size, same material, both have a hole on the side, one high and the other low. We test the boats and one sinks and the other floats. But just looking at the boats it can be difficult to see if we need to apply the formula that takes into account the air or not.
The lesson Nick gives is what we learned in school 20+ years ago. Density is important for understanding some aspects of material differentiation, for example, but not really why things float. The density explanation is sort of a shortcut answer, but doesn't really explain it.
Oh my god. I watched this to help me with an AP physics question about why things float with high densities. Dude i wanna email this to my physics teacher and just get out of answering this question. lol your channel is great. ALso my Algebra II teacher has the same clock as you :)
I already saw Videos about these subjects but yours are just Awesome totally worth the Time ! and a refresh is always a must !
I dig these old style videos of your channel more than the new ones. More fast paced talking, less try-to-be-funny animation. Keep up the good work, Nick.
It went too fast for most viewers.
Yeah me too
This is the most elegant explanation for a classical physics topic I ever heard. Thank you very much.
You're very welcome :-)
the term that i would use is displacement
thank you for the video. it really helped me with my project!!!!!!!!!
Excellent explanation. Spot on.
Excellent production!
Okey, I officially watched every single video i could see in your channel in less than week... (I'm new over here)... and i need more quantum mechanics!
Dang! That's a lot.
Your editing has gotten much better.
Well... weight is not the full story either, but you did touch upon the truth. It is weight divided by the displaced volume. E.g. A metal boat float because it displaces enough water to keep it floating, but fill that boat with water and the displacement become insufficient for floating, so the boat sinks. This can be simplified by observing the "displaced density" and comparing it to the liquid medium's density.
Density really matters. Density means average density. Even the density of water is 'average density' at molecular level.
I actually was taught buoyancy the same way; an object will sink into a fluid until it displaces its own weight of that fluid. If its average density is higher than the fluid, it never reaches that point and therefore will sink indefinitely until it encounters a medium that is denser than it. So, yes, density does play a role in buoyancy, but just a role. Saying density is the explanation for buoyance is like saying heat is the explanation for boiling. Yes, heat plays a part, but is not the central reason for the phenomena.
Ok, I'm in my 30s, and consider myself a smart guy, how am I JUST LEARNING THIS!?!??!?!?
You are smart mate. That's why you came here, to learn.
Well, you should realized why steel ships float. I guess you never asked, how the heck does big steel ships float?
Its due to displacement from weight.
jmitterii2 We we're always taught that because the average density (including the air in the ship) is less than water, that's why it floats
It happens to the best of us... actually no, the best of this know why things float.
I'm smart, but I still have so many questions. lmao... you are doing great brother... this is called life, and how we evolve in stages...
Floating or sinking still depends on the mean density of the object in question.
Your ninja ducky doesn't sink because he's hollow and this reduces his average density.
Is there actually a controversey here or are we quibbling over definitions?
Otherwise, this is a very good explanation.
+Andrew Stallard Yes, this issue comes up a lot in the comments on this video. Density is a nice convenient way (here on the surface of the Earth) to see if something will float. However, any time you find an "average" of any quantity, you're basically giving up on deeper understanding because average don't actually have physical meaning.
Averages are practical for answering "if" or "yes/no" questions, but are useless for fundamentally answering "why" questions. I'm just more interested in "why" things happen. As I've mention before to people in the comments, I'm open to creating a *weight* density since such a quantity would be more accurate than *mass* density.
@@ScienceAsylum I’m glad I saw this
You are great Sir.
love ur vids brotha. my teacher showed us this is class tommorow
TorabyehMusic I love to hear about my videos being shown in classrooms.
She showed it the day after you referred to it in the past tense???
wow.......just wow........i did't wanna see it first cause i was thinking it will be related to densities.....well i liked it a lot..thanks man
You're welcome :-)
0:00 science asylum was born .
I showed this to my mom, who is an upper elementary teacher, and she was not completely convinced. I figured I could try to make a simple experiment with a few more controlled variables.
If I changed the weight but kept density, surface area, and shape constant, then if one sank and one floated, than that would prove that density is not the cause. however, to change the weight, I need to change the mass (or the acceleration caused by gravity, but that is not easy) if I change the mass, I have to change the volume to keep density constant, but if I change volume, then I either have to change shape or surface area.
I could also try to change surface area while keeping density, weight and shape constant. However, if I change the surface area while keeping the same shape, then either density must change to keep weight constant or vice versa.
Since both weight and density are proportional to mass, and surface area is tied to volume, its hard to clearly disprove density in a simple experiment.
It is possible to change the weight of something without changing it's volume. You just have to let go of your need for that thing to be solid. A completely solid ball of steel will sink... but if you hollow it out enough, it'll float and still take up the same amount of space. That's how ships work.
First, Love the channel! I'm not sure how weight explains the function of a Galileo Thermometer. The temperature isn't changing the weight of the surrounding fluid. Any thoughts?
Weight still explains the Galileo Thermometer. I bought one a couple years ago with the intention of doing a video on it, but then it never happened.
I would argue it is density
But it isn’t “rubber” it is rubber and air which combined over that volume have a lower density than the water, but I fully understand that it is mass displacement
czcams.com/video/inPcQeYWVT8/video.htmlm7s
The reason things float is because the weight of the object is less than the weight of the fluid displaced by that object. That's why metal ships float; metal ships are not less dense than the water, rather the metal hull of a ship displaces more water than the ship weighs. Similarly, the rubber ducky floats because the shape of the ducky makes it displace more water than it weighs. Yes, it being filled with air helps it to float; however it's not because of the "average density", but rather because: the air helps make the overall rubber ducky weigh less than it would if it were solid rubber, and the enclosed air cavity prevents water from filling the rubber ducky (which would also make it weigh more).
If you were to cut the rubber ducky in half, it'd still float when placed on the surface; if water were to fill the inside of the rubber ducky, then it'd only sink once the weight of the water + the weight of the ducky weighs more than the amount of water the ducky displaces.
Matt S. thank you! just helped my understand the video better because you elaborated on something that while it was mentioned in the video - just wasn't quite enough of it.
So the size of the object (and maybe shape) affects its buoyancy?
@@matts.1352 I have a boat which weighs less than me. It floats when I sit in it. If you melt the hull of a metal ship to a cube, the cube will sink in water.
Science teacher's can use density to help explain floating if they make it clear that the density is regarding the entire OBJECT'S COMPOSITION and not the material the object is made out of. That rubber duck is made up of rubber AND air it it not entirely rubber. Hence the rubber duck object is not dense at all
Danielle Strachan What about something like a canoe? It's completely open on top. Do you just draw in some imaginary top? You don't have to do that if you realize it's not about mass... it's about weight. It's just a coincidence that, here on the Earth, those two are proportional. Yes, using density can be practical, but this video was more about the deeper understanding.
+Danielle Strachan
It looks like somebody else already raised my point.
I have believed the density explanation my entire life (47 years).
Density is also right, you have to measure duckies mass / volume , is way dmaller than 1000 ,
Density works with stuff thats not filled only pure.
And so, a legend was born.
Wait, if you try to calculate the resulting force bigger than zero, making the buoyancy minus the weight, it will implicate that the density of the liquid gotta be bigger than the object’s density. The duck just floats because of the air inside it, and if you take its weight and divide by the volume you could see that it is less than water’s density. By the way, love your videos!
Aweaome video buddy
thanks for explaining
You're welcome :-)
Finally someone that understands why things float. Has nothing to do with density or any fictitious force called "buoyancy". Things float due to gravity.
Why so???
can you make a video about centrifuge? How does it make denser particles move to the bottom of the tube? please
Density does play a vital role in this. The reason that a huge log will float even though it is heavy, versus a paper clip sinking despite it being light lets us know that weight is not the only factor. Density comes in because it measures a material's weight relative to its size. If you had a block of water and a block of wood of the same exact size, the block of water would weight more because it is more dense than the block of wood, therefore the log will float because the material that it is made of is less dense. Similarly, if you compare a block of steel to a block of water, the steel weighs more, so the paperclip will sink because it is more dense than a paperclip-sized area of water.
I think the confusion here stems from the difference between mass and weight. They are not the same. Density is related to mass, not weight, so objects have density wherever they are. They only have buoyancy if they have weight (something they don't have everywhere).
If you actually work through the math for something like this, it becomes even more apparent. Let's say you're talking about the floating duck... If you know the weight of the duck, how much space it takes up is completely irrelevant.
I suppose, like you said, you could explain it as the amount of WEIGHT relative to a certain size, but that's not "density" (mass/size). There isn't actually a name for weight/size.
Real Question. So i've got a can of coke (regular cos the diet one floats) and i wrap it with bubble wrap now it floats, but the weight has increased and the amount of space it takes up hasn't changed much so now is it about density? or is the simple fact that air weighs less than water in some sort of equation like
Sinks? (Needs positive value)= (Coke - Water) + (Air - Water)
and therefore because air
EastHamGirl11 The bubble wrap takes up space... so it has, in fact, increased the amount of space taken up.
I went white water rafting in Bali, it was so much fun
how does changing the temperature of the water affect buoyancy? For example. How do the thermometers with the floating capsules of fluid work? I used to think that as the temperature increased, the density of the outer fluid decreases. This could result in capsules that were previously less dense then the surrounding fluid to sink since they are now more dense. this is assuming that the capsules are all the same size and the ones with the higher temperature tags have more liquid and less air. I always assumed that, but I am not sure if this is the case.
The properties of the glass capsules inside do not change. They're completely sealed. It's the clear liquid they're floating in that changes (usually ethanol, not water). When the temperature rises, the ethanol molecules move farther apart, so the capsules aren't pushing as much of it out of the way. If they ethanol expands enough, it will weigh less than a certain capsule and that capsule will sink. The capsules are perfectly weighted to be in the middle of the container when the temperature of the ethanol matches the capsules metal label.
I'm amazed you didn't talk more about Archimedes! I def. thought your comedic side would somehow involve the "Eureka," story with him running down the streets naked!! I watched this documentary on NOVA about the "World's First Computer." They narrowed the invention down to a period between 200 years and came to that conclusion that ONLY ONE MAN IN THOSE 200 YEARS COULD HAVE INVENTED SOMETHING SO ELABORATE AND INTRICATE!!!! That was suchhhh a "wow" moment for me! This guy did inventions for fun!!!! “Give me a place to stand and with a lever I will move the whole world.” - Archimedes. So many of his inventions are still used to this day! The Archimedes Screw is such a valuable tool in 3rd World Nations. If you ever do videos on great people in history, he should definitely be a candidate! Side note: Although inventions he did for fun, math was his passion! They think he was using a form a calculus before Newton "invented," it. It is said that he was on the brink of something very important to him at the time of his death when he was killed my a Roman guard while scribbling "gibberish," on the sand.
History didn't really fit the flow of this video... also, this is a VERY old video.
That is the reason why even an object that would usually float can resist a buoyancy force if: this object has a perfectly flat surface and this surface has contact to another perfectly flat surface, like maybe a hollow glass cube in a glass aquarium. Normally, the cube might float on the water, but if you press it down on the flat bottom of the aquarium, there is no way for the buoyancy forces to attack, so it stays sucked at the bottom of the aquarium. Those buoyancy forces are also called hydrostatic forces.
There is a misunderstanding.
When we talk about "density" we are talking about the relation betwen the weight of the body and "total volume" (air and all other elements included) of the body in the water, not de density of the material.
How the sicilian scientist Archimede said "a body in the water is pulled up with a force equal to the weight of the water moved".
I got it about weight and pressure, thanks for the video I love all of them The Science Asylum.
But it's not clear what happens with the distribution (not sure if distribution is the best word) of the buoyant force. I mean, The bowling ball is not heavier than all the water underneath the ball (e.g. in the ocean), but still sinks. So, what happens there? Maybe a stupid questions but it's driving me crazy.
The bowling ball (say 16 lbs = 7 kg) is heavier than the water it's fighting with. It's heavier than _the water it's pushing out of the way._
The buoyant force is not equal to the weight of the displaced fluid, it is equal to the surface integral of the dot product of pressure tensor and surface normal vector. Try it with non-constant gravitational force, for example, a centrifuge force.
If, hypothetical we build a indestructible sphere (with total mass of just 100 mg) of 1m3 fill with interestelar vaccum (10^-17 Pa), how higher these sphere can go out with boyound forces? Like the dream of vaccum airships. If we build these sphere at space at same Pa, these sphere could be use to lift things from earth to space? How weight it could support?
Density of an object, rather than simply the substance, determines the ratio of the weight of water displaced with the weight of an object by determining the mass of the water displaced.
It IS involved, but as you said, most definitely not the cause.
Does this mean that if we pin an upside down bowl to the bottom of a water tank, and pump out the water and air trapped inside, it will stay on the bottom when letting go because of the weight of the water on top?
Can you perform this experiment? This will clearly show that pressure, not density, is the only thing at work here...
Woooooooah vid from way back
This is one my first videos ever. I had no idea what I was doing (but I _thought_ I knew).
I really enjoyed the “last, but certainly not least” double entendre.
2:21 Regarding objects filled with air, I remember the textbook in a physics class I took a few years specifically asking why this happened as one of questions in a lab assignment. I didn't know, so I asked. The teacher said that you need to take the average density of the entire object, including both the air and the outer material. If the average density is less than that of the liquid, it will float. Is this valid?
If you calculate the average density, then yes the rule will work again. It's a nice practical way to get to an answer, but it fails to answer the "why?" question. Averages don't have a lot of physical meaning. They're just a quick easy math trick. I addressed this a little in my math language video: czcams.com/video/inPcQeYWVT8/video.htmlm17s
@@ScienceAsylum Fair point. I'm finally taking a calc based Physics class, and learning how to use force diagrams and take into account all the different interactions instead of just averaging things does make things more meaningful. The explanation using weight and displacement definitely gives a much fuller picture than that of average density.
That said, I think averages certainly _can_ have physical meaning. What about center of mass, for example? My Physics book explicitly says that it's a _physical_ property of the object or system.
I agree that the center of mass has more physical meaning than something like an average density. While you can find the center of mass using a weighted average, that average is not where it's meaning comes from. You get a deeper understanding of its meaning if you find it using Newton's second law for rotation: Στ= Iα 😊
how then do you explain the floating of oil atop water ? secondly could you do a video talking about books you recommend (popularization and textbooks).
trimane mckenzie The oil weighs less than the water. Just like the ducky. As for the books video, that sounds like something I would put on my vlog... unless Audible decided to be a sponsor or something.
Im curious about the duck. could u answer this for me?
1. is the ducky solid? (not empty inside)
2. if u totally submerge the duck into the water and release, what will happen?
Im curious because the math should suggest density and the force should agree with each other.
B - W = (ρ_water) V g - (ρ_duck) V g = (ρ_w - ρ_d) V g
hence the sign of B - W should agree with (ρ_W - ρ) so the duck should sink, unless the duck shaped like a boat, or im very wrong about something.
Sir why the sideward pressure was same at 3:31.... please?
Since pressure increasing with depth is the reason why the net force is upwards, then does that make this very similar to gravity with time dilation?
Similar, yes. In fact, you can model a bubble as if it has negative mass with an upward gravity. It's kinda cool 🤓
In "is maths the language " video, ninja ducky has a density of 291kg/m3? The volume of a cup which just floats would have the same density as water. That is volume of cup wrapped in cling film say. If a similar cup floated above the water surface it would be less dense.
Its like: iron is more dense then water, so sink; but if you make a boat of iron, then will float. It depends on how much space he moves the water
(Average) density *is* the way to go, you just need to use your head about what all is to be considered while calculating it.
czcams.com/video/inPcQeYWVT8/video.htmlm17s
@@ScienceAsylum It does have meanings, because it gives you (total mass submerged)/(total volume submerged), and that's exactly what decides if the object floats/sinks.
"If the full volume goes into the water, how much mass goes in? Is that mass lesser than that of the water displaced? If yes, it will float. If not, it will sink. If they're equal, it will stay there."
That's the process that one will go through when determining whether it will float or sink.
But then isn't that the exact same asking "How does the object's *average* density compare with that of water's?"
Edit: I'm taking about the situation in a location with uniform gravity. So mass/weight are interchangeable.
Things that go into the water in a vertical position (for example a wooden butter knife) and are pushed to the bottom and come back up, why do they come up shifting into a horizontal position.
The same reason the butter knife would lay horizontal on the ground if your dropped it. If it's vertical, it's center of mass is higher, which makes it little more unstable... but if you could put it in the water PERFECTLY vertical (no slant in the knife, table, floor, etc), it should stay that way until something knocks it over. It's a lot easy if you shift the center of mass lower into the water by hanging something heavy from the bottom.
To be clear the air can within the boat can be considered it’s volume which reduces overall density drastically?Please explain?
czcams.com/video/inPcQeYWVT8/video.htmlm17s 🤓
Really appreciate your efforts of going through comments and answering petty questions,feel guilty of getting all of it for free,Will support when I will start earning!!😅
The Science Asylum words can be daunting sometimes!
Answering comments is really important to me, but it's difficult to keep up sometimes.
Is it possible to create a surface geometry where the horizontal forces don't cancel and you get a net horizontal motion?
Sure. Just accelerate in a car with a helium balloon. The buoyant force from the air will be partially horizontal: czcams.com/video/y8mzDvpKzfY/video.html
This video is a battle of "Umm, actually". I guess there was not enough focus on the idea that density only makes things float on Earth where there is gravity, so it must be weight that makes things float, as weight does not work in outer space where things no longer float.
(this is not me trying to fix the video, but maybe help new watchers before they dive into "but average density" comment section)
Also: Sir, you have half million subs, you are not allowed to respond to comments on your 8 year old video :D (it's so awesome to see this comment section with posts old and new and most of them with replies).
I'm not _allowed_ to respond? 😂 Anyway, I agree I was extra pedantic in this one. Honestly, "extra pedantic" was kind of my MO back in the old days. I hadn't settled into the nuance yet. (That being said, I appreciate your constructive criticism. Thanks for not being a jerk.)
Ok, have to stop trying to make a good response. Just want to say, after 10+ years of watching popular science, I'm really happy to find this channel and I enjoy going through the whole list.
So only tiny explanation, by "not allowed" i mean "how do you do it, are you magic?"
And lastly, I was trying to rather target the comments, I realize it would be really hard to be properly nuanced in 5-minute video, especially one of the first on the channel. See you in a few months when I catch up with "today".
@@HeroDarkStorn Comments are an important part of the CZcams experience, at least for me. I try to answer comments whenever I can. I'm also pretty good about monitoring my comment sections so they can be a positive experience for everyone.
You said the water has more weight that the ducky (3:00) but the dispalced fluid can only ever be equal to the weight of the water displaced otherwise the ducky would be accelerating upwards, not floating. I'd say it is essential that we use density, but as 'density of the entire object, including all the materials that it is made up of' to explain archemedies principle. It is the average density that must be less than or equal to the density of water dispalced for it to float. The average density of the duck can not be 1100kg/m3 - that will really confuse people! Thanks, please reply and rip apart my explanation :)
+sirchristopher2000
The problem is this: What would that "density of the entire object" even mean? It would be an average and averages don't have physical meaning. They're just convenient math tools to simplify our work. Yes you could find that number and yes it would be less than the 1100 kg/m3 and yes you can use that fact to SAY the ducky will float... but you will have lost the deeper understanding of WHY the ducky floats. That's what this video is about :-)
If you wanted to use a density, it would need to be a weight density instead of a mass density because buoyancy is about forces, not about mass. You'd have to measure something in "Newtons/cubic meter," but we don't have a name for that kind of measurement.
Why are the pressure vectors upward? Is it supposed to represent the water pushing the ball upward? Wouldnt, if you put the object very close to the bottom of the fluid, the force pushing it up be smaller than force pushing it down, andso it would sink?
Pressure is exerted on all objects that are immersed in a fluid along every vector perpendicular to its surface, as the fluid itself wants to occupy that space. You are also correct, at a sufficiently low depth, objects that normally float will start to sink. For an average human in water, this happens around 10 meters depth
@@snowthemegaabsol6819 huh? i found out why objects tend to be pushed up in a fluid, this is because the deeper in a fluid you go, the denser it gets. essentially its just 10 atoms pushing you up and 8 pushing you down, so netto is 2 up.
What i ment is if something like a bubble is down at the bottom of a container, there should only be liquid exerting force from the above-ish area, none from below, so why does it still rise?
answer i got so far was because of microinfluences like local temperature change or pressure change
To answer that requires considering all of the directions from which the object is experiencing pressure. The net force may be up, but it's also being pushed at from the sides. Liquid is wanting to get under the object from the sides as well, not just from under, so given the opportunity, liquid will rush under the object from the sides. Even if a bubble is at the bottom, liquid can still get under and float it back up.
There are ways you can get a normally buoyant object to stick to the bottom, though it depends on how strong the buoyance is, the shape of the object, the fluid used, and the smoothness of the surfaces involved. A coaster for example, if you found one that was buoyant in water and put it at the bottom of a smooth bowl filled with water, it wouldn't float. On the contrary actually, it would be stuck very firmly
Gravity is what makes things “float” in water. Things go from high to low. If you were in the ocean the deeper you go the more weight there is from the other water on top of each other which forces a less dense item such as a boat made of iron to stay above the water, if you have a solid bar of iron and throw it into the water it will sink.
This also explain why some type of wood is denser than water but it floats
Thats why you feel the rocks are lighter under the water
I believe that the steel in huge ships way more than water. If you made a huge tank filled with water that was large enough to fit in a ship, the weight of the ship would be greater than the water unless the water was extremely deep.
Ships float because all that weight is displaced. But if you get a gallon of water and compare that to 1 gallon of steel the steel would be heavier. So actually it is about density.
It doesn't matter how much water you have against how much steel you have, solid steel can't float in water. Ships float because they're not solid, they have empty corridors and rooms everywhere, so there isn't as much force from gravity per force of buoyancy from the water.
Density and buoyancy is a very superficial relationship, not a mechanism of action, and is limited to the surface of a fluid. It can't, for example, explain why an average, normally buoyant human will sink at a depth of >10 meters
At what depth does the bowling ball stop sinking and become buyont? Am I understanding this?
Some bowling balls actually float on water. There used to be an annotation explaining this, but YT got rid of annotations. I need to go through my old videos and replaced annotations with pinned comments, but haven't gotten around to it yet.
I don't really understand the 'battle for supremacy'. You say that the water is heavier but going back to densities (I'm sorry, don't hate me) if the duck has a higher density than the water then in that same volume it will have more mass than the water does and if weight = mg then how can the water be heavier?
Hold up you mean to tell me 8brubber duckies is a newton?
Very likely. Anything that is 102 grams weighs 1 Newton on this planet.
The go to example people like to give, is that an apple weighs 1 Newton, as an homage to the legend of Newton's apple as a way to remember it. Most apples in my experience are heavier than this, and are more like 1.5 to 2 Newtons.
Wait .. the ninga thingy has air in it .. did you include the volume of the air while measuring the density?
czcams.com/video/inPcQeYWVT8/video.htmlm51s
Is ninja-ducky rubber all the way through, or does it have air inside? P.S. I am not nerd-clone
Really love your videos btw
Whether something will float or not does depend on its density.
But contrary to the popular misbelief it doesn't depend on the density of the substance the object is made of but rather the density of tge object. For example : a hollow iron box with thin walls will float on water even though iron is more dense than water. That's because the density of the entire box is less than the density of water
I addressed this detail in a later video: czcams.com/video/inPcQeYWVT8/video.htmlm17s
well ninja ducky isent completly soft rubber but contains air so the full density of the rubber duck becomes less, so the dencity rule still counts
watching this in *1.5 so fkn epic !
Wow! Most people have to set my older videos to 0.5x.
lol, i'm not surprised.... actually i thought it was natural at first, then i realised i had watched an instructional video in 1.5 just before your video..
I saw Mark Rober float things in liquid sand; that was cool
That was a great video. Physics Girl did one too.
So density itself isn't what causes objects to float or sink, but by taking an object that sinks on its own (like a huge sphere of steel) and increasing its average density by hollowing it out, it can be made to displace a larger volume of water and float (like a battleship made from the aforementioned steel). So therefore doesn't average density make an object sink or float by contributing to buoyancy? Because an object with a higher average density than water will always have more mass than of the volume it takes up in water, and therefore will always weigh more than the water it displaces. So density isn't the cause of an object's floating or sinking, but an object with a higher average density than the fluid it sits in will always sink, and an object with a lower average density than the fluid it sits in will always float.
I responded to comments like this about a year ago: czcams.com/video/inPcQeYWVT8/video.htmlm17s
The Science Asylum Thanks for the reply
wait im so confused >.< i was taught and teching my self that buoyancy had to do with density...but it doesnt? im doing a project on how the force of buoyancy and gravity interact im just going to write down everything on my mind maybe you can answer some questions or prove me wrong? (sorry about spelling) -changing experement to using different objects with different densities
how do you make something less dense
I know what makes a boat buoyant but how do you make it more buoyant
(the space displaces the amount of water that should be there and there for the buoyant force is greater then the force of gravity
to make a boat more buoyant (Archimedes principle says that a object buoyancy is equal to the amount it displaces so if boat is sinking, to make it float you would need to displace more water that is equal to the amount it displaces so to make a boat more buoyant you would need to displace an amount more or equal to the weight.
To make a ship more buoyant you would need to make the amount of displaced fluid larger (the space larger)
In order to make something more buoyant you would need to make it less dence then the water
It doesn't really have to do with density, no. Basic science classes teach it that way because it keeps things simple for people and it gets the point across most of the time. Unfortunately, it's an over-simplification. Archimedes principle is better.
In chemistry, they're usually dealing with two simple fluids. If you determine which has the lower density, then you know that one will sit above the other. This also works if you have a floating solid like wood. However, just because something tells you if something WILL float, it doesn't mean you've discovered WHY it floats. It's a subtle but important distinction if you have something like a rubber duck or a boat. In those cases, you need to Archimedes principle to explain what's happening. It's not about a boat's density. It's about how much water it's displacing (pushing out of the way).
The displacement of water wouldn't even matter if the water didn't have WEIGHT. If you wanted the boat to make sense with density, then you'd have to include the empty space inside the boat as part of the boat... which is kind of silly. I mean, you wouldn't include the empty space inside your mouth as part of you. The number you got for the density of the boat (including the space) would have no purpose or meaning other than to tell you if the boat floats.
@@ScienceAsylum "If you wanted the boat to make sense with density, then you'd have to include the empty space inside the boat as part of the boat... which is kind of silly. I mean, you wouldn't include the empty space inside your mouth as part of you. " But I have to include the empty space inside the boat as part of the boat to calculate its weight too. There's no way to find out if the boat floats without considering the air inside as part of the boat. If the boat was filled with cargo instead of air, that cargo is also part of the boat and might cause it to sink.
my floating story is that one time i was eve`s dropping on a story(of my friends) but i was not understanding it wheen i asked them what it was they were talking about they said that i was floating on their conversation ....hhow funny
Vedios coveys what u want to say but i get conveyed only when though your replies on the queries. Thanks. You are really gpod
does this apply to the tower of liquids experiment?
Yes, it does... it's just that picturing what's happening is more difficult.
i guess it's beacause we use liquids instead of solids.
It's like trying to do the same things but with a smaller unit so it's more abundant and therefore REALLY hard to picture
But since when an object goes all inside the water, the weight of the water moved is "object volume x water density" and the weight of the object is "volume of the object x density of the object" you can cancel out the volums and you are left with the density.
But yeah, since it is net density that you have to count, the concept doesn't really make sense
This seems to be the first video on the channel but there says at the end "previous videos", so, this isnt the first?
Never thought about that way. But it makes me sad that ninja ducky lost. Water is too op
I'm still finding it a little hard to understand when you bring weight into the equation.
Suppose I toss a 15 pound ball of ice and a standard US penny into a wishing well (containing sufficient water to drown a man), the ball of ice will float, while the tiny penny will sink. How does this work now?
the object displaces a volume of water equal to its weight. So a 15 pound ball of ice will displace a volume equal to 15 pounds of water. Since the volume of 15 pounds of water is less than the volume of 15 pounds of ice, the ice floats.
The penny on the other hand is not large enough to displace its weight compared to its volume of water, so it sinks. If you curved the penny into a boat shape with enough air in it, its volume could become large enough to displace a volume of water equal to is weight without sinking.
Basically, for an object to float, its volume must be large enough compared to its weight to displace a volume of water that is equal to its weight. If the volume isnt large enough to displace its weight in the volume of water, then it will sink. If its volume IS large enough to displace its weight in the water, then it will float. Changing the shape of the object can allow it to displace more water without changing its weight.
2:17 runner's density is greater than water but ninja duck is not. It is filled with air, so the average density is less.
Average density might be useful, but it doesn't really have any meaning: czcams.com/video/inPcQeYWVT8/video.htmlm17s
I have one problem with this explanation. I am a diver and when underwater, if I add gas to my BCD (Buoyancy Control Device) I am changing volume of gas bags inside. My mass doesn't change. Just volume ergo density.
It's not really mass either. It's weight. If the volume of air increases, then it's displacing more water. It's _weight,_ not volume.
The reason why Ninja Ducky floats is because
A- The volume of the water that Ninja Ducky displaces weighs at least the same as Ninja Ducky.
Or B- Since Ninja Ducky has air inside of him, the average density of Ninja Ducky is less than that of the water, so it floats.
I would posit that (B) isn't really an option because the average value wouldn't actually have physical meaning: czcams.com/video/inPcQeYWVT8/video.htmlm17s
I demand more Ninja Ducky!
Help science asylum...Can I ask a serious question.
Take the titanic as example. On a good day it floats. But lets say that I crush the titanic into a ball and then place it back into the water, will it sink or float. Remember the weight has stayed the same but the density hasn't.....
MyPLAnksCoNsTaNt It'll totally sink. For the record though, the boat's density is still the same. It's still made out of all the same stuff. However, it is no longer displacing enough water to float. The water it's pushing out of the way weighs less.
@@ScienceAsylum The boat density is not the same, you must account for the AIR inside the boat when calculating density! you are obviously very smart it is shkckng to hear you mistake this point.
0:36 sounds like beggining of rap: rhymes like violation-education
Is ninja Ducky solid mass right through or does he have air in the middle. If he was solid rubber right the way through he would sunk, right?
+adun6899 Yes, there is an empty pocket in the middle. Solid rubber would definitely sink... but then, of course, solid rubber would be heavier.
I think it will be more appropiate if the word density is replaced by the average density.
In my school textbook, it states that the steel ship will float in water because the ship is mostly hollow and contains air. The average density will less than that of water and so the ship floats.
czcams.com/video/inPcQeYWVT8/video.htmlm17s
It's cool he has a Pink Floyd T-shirt on too! :D
If only this video had one more example- a light floating object
I ALWAYS knew Nick had magical weight hands.
Hey,,u r. Changing my every topic concepts ,,,I have to update my topics now ,, however ur videos are always great 👌👌👌
I have a question, I see it's because of the weight of an object,. But in vacuum things fall the same velocity, so is their weight equal?
Weight has nothing to do with the air. Weight is the pull of gravity. Gravity would exist on Earth with or without an atmosphere.
@@ScienceAsylumI see, what I'm confused about is, if in a vacuum, 2 different things, a hammer and a feather for example, fall at the same time, what makes the hammer heavier the the feather?
@@V1C.T0R bem dito!