What is Underwater: Definition and 152 Discussions

The underwater environment refers to the region below the surface of, and immersed in, liquid water in a natural or artificial feature (called a body of water), such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.
Liquid water has been present on Earth for most of the history of the planet. The underwater environment is thought to be the place of the origin of life on Earth, and it remains the ecological region most critical to the support of life and the natural habitat of the majority of living organisms. Several branches of science are dedicated to the study of this environment or specific parts or aspects of it.
A number of human activities are conducted in the more accessible parts of the underwater environment. These include research, underwater diving for work or recreation, and underwater warfare with submarines. However, the underwater environment is hostile to humans in many ways and often inaccessible, and therefore relatively little explored.

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  1. S

    Can you close a car door underwater?

    Hi there, I was wondering if it is possible to close a car door underwater? I understand that, due to differential pressure, you cannot open a car door until the pressure equalises. But is it possible to close a car door underwater? Sorry, I know it must sound like a rather silly question...
  2. Boccadoro

    The challenge of transmitting radio frequencies underwater.

    If both a transmitter and receiver antennae were submerged, and within a defined range and depth, what range might be available to a civilian operator? Are two divers able to communicate by radio? B
  3. IamDev

    Help with torque calculation of underwater rotating disk?

    Hello Guys, I have a disk of diameter of 150mm and thickness of 10mm which is rotating at the constant speed of 100rpm. The disk is inside water which is approximately 4-5 cm below the surface. Disk is horizontal (parallel to the water surface). Disk is attached with the shaft of the motor. At...
  4. B

    If the double slit were performed underwater?

    I know that photons interact weakly with air molecules which is why we have the interference pattern, and I know they interact strongly with say mud so there would be no pattern in a mud pit, though I am not sure if in a mud pit there would be any kind of light that reaches the screen at all...
  5. Y

    Why does temperature decrease with depth underwater?

    Seems like an easy question yet I can't find an answer. Obviously the surface layer of the ocean gets more sunlight but I don't think that is the reason deep water is colder. The increase in pressure usually increases the temperature but this seems to be the exception. Thanks for taking the time...
  6. X

    Catenary shape of a towed underwater cable

    Hello, I'm designing a towed underwater vehicle (towfish) and I am having trouble with determining cable tension at the length of the cable at given depths and speeds. I have estimates of vehicle drag at speeds up to 4 m/s and the vehicle weight in water is known. Its really just the...
  7. U

    Can underwater pressure be equated with weight? (after conversions)

    It is a established fact that pressure i.e ρgh will be same at a given depth. Suppose in a tank filled with water the gauge pressure works out to 1 bar, then the total pressure at the depth of tank would be 1 bar + 1 bar atmospheric pressure = 2 bar pressure. 2 bar pressure equals 2 kgf/ cm2...
  8. I

    Underwater oxygen extraction device

    Hello everyone. I'm sure there is a really good reason as to why this hasn't been done yet but I just wanted to ask and see if it could be done. Why can't we make a mouth piece that basically takes in water, filters out the oxygen and then expels the water back into the ocean, then takes in...
  9. Y

    Help Needed: Delivering Substance 300' Underwater Without an Engineering Degree

    Hello, new here looking for some help on a project I'm working on. First off, I am not an engineer, have no degree in anything and am a math moron. This is what I'm trying to achieve: deliver a proprietary substance overtime in 300' of water. The fantasy is to use Co2 gas to propel the...
  10. S

    Question regarding underwater pressure

    Hi, I am having some argument with my friend over the following elementary physics problem: Assume there is a pressure sensor located at position C underwater and deep enough, and assume also the water is completely still. If there is a helicopter or hovercraft idling above the water, will...
  11. Y

    Forces on an underwater vessel

    I have a question about a Fiberglass Hemisphere that is 16" in diameter and 8 " in height. It is being used as a vessel under the water so it has a closed top. I wanted to know how to figure out how much stress from water pressure it will handle before it fails. thanks!
  12. F

    Ultrasonic transducer for standing waves underwater

    Hi I'm not too sure where to post this but since I am, after all, doing a project under the EE department, I thought this might be the best place. I'm new to acoustics, so what I know is rather minimum. I'm trying to look for ultrasonic transducers that can manipulate objects...
  13. J

    Light in Underwater Pool Refraction Problem

    Homework Statement A small underwater pool light is 1 meter below the surface of a swimming pool. What is the radius of the circle of light on the surface, from which light emerges from the water? Homework Equations Snell's Law Fermat's PrincipleThe Attempt at a SolutionI have no idea about how...
  14. M

    How do you stop rusting if an iron object is already underwater?

    I have a bit of basic knowledge on rusting and corrosion of iron but I am trying to find ways to stop rusting. The problem is what if an object was already submerged in water? Is it still possible to stop it from rusting? I know there are 3 ways of preventing corrosion but I am not sure if there...
  15. S

    Buoyany and change in volume underwater

    By breathing in deeply, you can change volume of your body. Suppose a swimmer underwater weighs wf = 23.4 N with his lungs full, and we = 48.0 N with lungs empty. Find change in body volume when swimmer inhales. I know the apparent weight = weight in air - buoyant force and buoyant force =...
  16. F

    Measuring Color Underwater: Techniques and Challenges

    Hello, I want to measure color of some objects underwater. I believe that one way of do that would be using the RGB system on photos. The other way would be measuring absorbance directly with an spectrometer, but I don't know how I can standardize my conditions. I have to measure the color of...
  17. M

    Underwater projectile affected by Coriolis Effect

    If I am trying to fire a torpedo at another vehicle underwater do I need to worry about the Coriolis Effect? The speeds that torpedoes travel at are approximately 20 m/s and have a maximum range of around 10km.
  18. G

    A bullet shot underwater given a velocity function

    Homework Statement A bullet shot underwater will experience "viscous drag" and follow this velocity equation. vx(t)=voxe-bt What is the maximum position of the bullet (if you were to wait a long time, what will its position be)? Given: vox=247m/s b=0.53 s-1 x0=47.9m Homework Equations...
  19. M

    Calculating weight of underwater object given normal force

    Homework Statement A glass ball of radius 2 cm sits at the bottom of a container of milk that has a density of 1.03 g/cm^3. THe normal force on the ball from the container's lower surface has a magnitude of 9.48 * 10^-2 N. What is the mass of the ball? Homework Equations Normal force +...
  20. L

    Transmitting video from underwater

    hi. I am looking into buying/making a wireless video camera to attach to a radio controlled submarine. I am familiar with the 2.4g cctv type spycams and digital video receivers but am told water is an insulator to the fm signal being transmitted. I am also aware of the rc 12 wireless mini cam...
  21. D

    Force due to a submersible water pump to move an underwater vehicle

    Homework Statement I'm trying to find the force exerted by a 500 GPH (gallons per hour) submersible bilge pump. My team is designing a submersible vehicle for our university course. The vehicle is only supposed to move up and down in the vertical direction; basically it should just be able...
  22. D

    Can a Paraglider Survive Eight Days Underwater?

    Here: http://news.yahoo.com/video/oddnews-22772304/odd-news-paraglider-vs-bird-double-double-delivery-8-day-dive-record-27140303.html Skip the feathers. I applaud the guy. True, just a few feet, but he's on SCUBA, so sleeping? Gosh! Never did that. Took a few micronaps in my day...
  23. M

    Changes in pressure underwater

    If one was say 10 meters underwater but in a cave-like system, would you experience the same degree of water pressure compared to being 10 meters under open water? And why would this be? Any help much appreciated, diagram attached as not sure if question makes sense
  24. P

    Why Does Sound from Above the Surface Sound Faint Underwater?

    When swimming underwater, why does sound from above the surface sound very faint? I know that the answer to this may be simple, but I just can't put my finger on the answer. I know that sound travels faster in water then it does in air, does this fact have anything to do with it? Thanks!
  25. L

    Array of underwater transducers for sound massage

    hello, since a while my mind is caught by an idea. This idea is concerned with underwater sound massage system. For this purpose i would like to build an array of underwater sound transducers, which can all be steered individually (to do a coarse beam forming). However, since i am...
  26. T

    Containing Electrolysis Underwater

    If the process of electrolysis is contained underwater would it work like it is supposed to?
  27. M

    Flowfield visualization of a gun shooting underwater high speed video

    I ran this experiment to find out what a gun would look like while shooting under water. Turns out to be quite interesting. The muzzle blast is NOT spherical as I first assumed. Regards, Mrpennywhistle
  28. J

    Underwater Pressure on Sphere Dilemma

    Dear Friends, I have a problem that has been driving me nuts for months now, and I am hoping you guys can help. I need to understand whether: 1. The Force with which a hollow, buoyant Steel Sphere is propelled upwards from under water at significant depth changes as the sphere ascends to...
  29. E

    Bullet shot underwater where do the bubbles come from?

    Homework Statement Hi, A gun totally immersed underwater and shoot a bullet. Q1. Would there be a trail of bubbles behind the bullet? Q2. If there are bubbles, where do they come from? Q3. If there are bubbles, would the sum of the volume of all bubbles be equal to the volume of...
  30. C

    How Did Engineers Construct Submerged Tunnels Like BART's?

    How did engineers manage to build tunnels submerged 100 ft under water without having tunnels collapsing? Say for example, BART, has trains going through these tunnels daily. How did engineers build water tunnels?
  31. M

    Breaking the sound barrier underwater?

    I know it may not even be mechanically possible to reach the speed of sound underwater (1,484 m/s); but this is just a theory. After discussing with several people, what would happen if a submarine was to break the sound barrier underwater, a couple of interesting theories arose. Going...
  32. T

    Does temperature affect a spring's properties underwater?

    Hello PF! I was having a debate with a coworker of mine. We were talking about the properties of springs underwater. He was convinced that it doesn't change, at least when in water. I thought otherwise. Does a spring's spring constant change if fully submerged underwater? Does the...
  33. R

    High frequency acoustic waves underwater

    Hi, was just wondering if anyone could help me out with this query, I'm just curious to know why high frequency acoustic waves are greatly absorbed underwater? Thanks in advance.
  34. D

    What is the Maximum Weight of a Concrete Block Underwater?

    Hello, I would like to ask if my calculations are correct and which approach I should use if the answer is correct (I apologize if my calculations look ugly, just joined this forum). Homework Statement On land, the maximum weight of a concrete block you can carry is 25kg. How massive block...
  35. M

    What effect does a nuke have underwater?

    So I was watching Abyss the other day and got to the part where Ed Harris drops down an underwater cliff to disable a nuke which lies at the bottom. I think the distance was two miles underwater. If the nuke were to have exploded what kind of damage would be done and would it have even been...
  36. A

    Understanding Underwater Pressure: Exploring Multiple Hulls and Structures

    Ok I am almost positive this doesn't work or it would be used in deep submersibles, but I am at a loss as to why. About every 33 or 34 feet pressure underwater increases by 1 atm. So a submarine at 33 feet under water with 1 atm internal pressure would have 2 atm of external pressure...
  37. Math Is Hard

    Underwater Hotel Room in Fiji: Live Like a Sea Monkey!

    Wouldn't this be super fun...? http://stylefrizz.com/200802/poseidon-underwater-hotel/ ...I mean... at least for the first 3-4 minutes before the claustophobia kicks in and you start hyperventilating and clawing frantically to escape. But if you're into this sort of thing, you and...
  38. tiny-tim

    Music Underwater musical instruments?

    i was pondering why no fish have ever become famous musicians :confused: when it occurred to me … are there any musical instruments designed to be played underwater?
  39. R

    You are looking up from underwater in a swimming pool radius of circle?

    Homework Statement You are looking up from under the water in a swimming pool. If you are 2m below the surface, what is the radius of the "hole" at the water surface through which you can see out of the pool? Homework Equations n.sin(theta)1 = n.sin(theta)2 The Attempt at a Solution...
  40. K

    Underwater Express power and propulsion

    I am fascinated with the idea of supercavitating subs, and DARPA's underwater express program has caught my fancy. A sub that can go faster than 100 knots submerged, now that is too cool. I am curious as to speculation on how Electric Boat will power and propel the ship. The idea I personally...
  41. FeDeX_LaTeX

    Do Electromagnets work Underwater?

    Hello; Just a question that I have been thinking about. Is there some reason why they wouldn't work in water? Thanks.
  42. B

    Newtons from Bouyancy underwater comparing helium, oxygen, and hydrogen

    I have an under water application where I need the maximum amount of buoyancy with a limit to the volume i can use for a lifting device. My question is how much more Newtons would be exerted for helium instead of oxygen, or hydrogen instead of oxygen underwater? What is the percentage...
  43. H

    Installing Underwater turbines

    I'm doing a feasibility study on installing underwater electricity generating turbines. Being a civil engineering student, I don't know much of anything about the electrical engineering aspect of this. Now, these turbines are supposed to be near the bridge so most of the cables will be run along...
  44. H

    How far does sound travel underwater?

    Hi, How far does sound travel underwater, and more importantly does it travel further in water than in air? If so why? I know that sound travels faster through water than air for obvious reasons (density), and I intuitively assume further, but I cannot explain why. Any help is appreciated. Thanks
  45. S

    Underwater data acquisition project

    I'm currently working on a project where I am required to measure the load that is applied to a chain, which is submersed in an underwater tank (approx. 20 feet). The entire assembly must be self contained and hermetically sealed for up to 6 months. I've successfully sourced some good ip68...
  46. C

    Energy created by a balloon released underwater

    How much energy (Watts?) would be created by a balloon that was released under water? I am picturing a scuba diver's inflatable vest (a BC) that is suddenly inflated (assume zero air inside to begin with). Or more accurately if you have ever seen a free-diver who swims down a few hundred feet...
  47. N

    Designing a autonomous underwater vehicle

    am designing a autonomous underwater vehicle .well,i got 2 issues right now regarding its buoyancy control and water proof joints. can anyone suggest me some ways by which the buoyancy can be controlled and some methods to make the joints of auv water proof efficiently.
  48. V

    Pressure Underwater Homework: Calculate Force for Submarine Porthole

    Homework Statement (a) Calculate the absolute pressure at an ocean depth of 500 m. Assume the density of sea water is 1024 kg/m3 and that the air above exerts a pressure of 101.3 kPa. --I got this one its 5118900 Pa or N/m (b) At this depth, what force must the frame around a circular...
  49. L

    Density of water underwater

    Homework Statement Estimate the density of the water 5.3 km deep in the sea. (bulk modulus for water is B=2.0 *10^9 Homework Equations \DeltaV/V=(-1/B)*\DeltaP dP/dY=-\rhog The Attempt at a Solution I tried to use the equation: P=Po*e^(-\rhoo/Po)*gh But i kept getting ridiculously large...
  50. N

    Bubble rising underwater. What is the time taken for it to reach the surface?

    Homework Statement The initial volume and depth of the gas bubble is V0 and H respectively. The bubble has a mass M and the gas can be assumed to be ideal. The gravitational field strength is a constant g. And the density of water is Dw. What then, is the time taken for a bubble initially at...
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