What is Underwater: Definition and 153 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. cambeaux

    A Pressure on a Capsule within an Enclosure (Underwater @ 500m)

    For this engineering project I am trying to understand how the pressure would be distributed (if at all) throughout the enclosure. It will be at a depth of 500 meters (4888 kPA). It is designed with a stainless steel enclosure which can withstand the external pressure at this depth. Inside is...
  2. S

    I Does being surrounded by water affect collisions between 2 bodies?

    Imagine there is a square plate fixed at the edge on all sides, it is impacted by a body with a pre-determined kinetic energy. Now assume that this plate is submerged in water and impacted by an identical body with the same amount of kinetic energy. Will the results be different? How to...
  3. Lieutenant Barclay

    Titan implosion: underwater shockwave?

    Like many I’ve been captivated by the Titan story. I’m wondering a few things: 1. Was a shock wave cause by the implosion? 2. Would marine life have been killed similarly to “fishing w/ dynamite”? Kill radius? 3. A TV talking head claimed the inside of the vessel would have heated to “a temp...
  4. C

    Does Depth Affect Buoyancy Force on a Spherical Object?

    For this problem, The solution is, I agree with their solution from Archimedes principle, however, if I look at the equation ##PA = F##, where ##A = 4\pi r^2## and ##F## is the force over the entire apple assuming it is spherical. I thought the pressure will increase with depth and therefore I...
  5. Astronuc

    Vanuatu - East Epi underwater volcano eruption

    https://www.cbsnews.com/news/vanuatu-underwater-volcano-erupts-east-epi-warnings/ The volcano lies 68 kilometers north of the capital Port Vila.https://volcano.si.edu/showreport.cfm?wvar=GVP.WVAR20230125-257060
  6. S

    I Behaviour of Magnetic Fields Underwater

    I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean. There is an awful lot of conflicting information online. Ultimately, I'd like...
  7. L

    Apparent depth of an object underwater

    I would know how to solve this problem if the person had been standing pratically above of the object underwater by using Snell's law and the approximation ##\sin(\theta)\approx\tan(\theta)## fopr ##\theta## small, but in this case I don't see how to find the angles ##\theta_1## and ##\theta_2##...
  8. N

    A Underwater acoustic unit conversion

    Hi all I have acoustic noise level value in dB vs 1 dyne/sq cm e.g. -10 db vs 1 dyne / sq cm. I need to convert it into dB ref 1upa unit. How i will convert it? Thanks & Regards
  9. L

    Image position and magnification for underwater spherical lens

    Using the data given and recalling that in this configuration ##R<0## I get: ##\frac{1.33}{0.5}+\frac{1.5}{q}=\frac{1.5-1.33}{-0.2}\Rightarrow q\approx -0.427 m=-42.7 cm## so the image is virtual and is ##42.7\ cm## to the left of vertex ##V##. The magnification is ##M=\frac{n_1 q}{n_2...
  10. C

    A kind of strange Underwater Air Bubble question

    Hello, Something I’ve wondered about is those amazing air bubbles that are sometimes found in underwater caves. In particular, I was wondering how the depth of the water does or does not affects them. In my Figure 1 example, the water is 50 feet deep and air bubble in the cave has 3 feet of...
  11. Astronuc

    Underwater avalanche in Congo Canyon lasted two days

    https://www.bbc.com/news/science-environment-57382529 5 m/s is about the speed of cooling water in the core of a PWR. It's not very fast, 16.4 ft/s, or 11.2 mph.
  12. N

    Source Level calculations of an Underwater Cylindrical Acoustic Array

    Hi all I am trying to calculate Source Level 'SL' of a underwater acoustic Cylindrical Array with multiple Transducers. The array has 03 Rings with 32 transducers in each Ring. The spacing between each ring is around 0.18m whereas Dia of each Ring is about 1m. Each transducer is being driven...
  13. yourheartandsoul

    Finding the force on a camera window underwater

    I figured out that the pressure is 8.0442x10^7 Pa and I’m not sure how to approach the second half of the question. I’m thinking I use the formula F=PA but I’m realizing it’s not saying that .15m is a diameter or a radius.
  14. M

    Fooey, 'Underwater' is not the movie I hoped it might be....

    I finally saw Ford v Ferrari, and one of the shorts opened with a team of people working seven miles under the ocean. My immediate, very excited, thought was that they've made Peter Watts amazing novel, Starfish, into a film. Starfish is the first in Watts' Rifters trilogy, and I loved it...
  15. H

    Need stress value of aluminium for project work

    Summary: I am not a physics student but I really need to prove that aluminium will not deform 10m underwater Hi I am doing a project of a product which will sink underwater. It will be a sealed cylindrical vessel, length 2m, width 1m, thickness 0.02m. Aluminium 6061t will be used with a yield...
  16. I

    Underwater thrust formula?

    I'm trying to determine the force needed for one object to displace another object underwater. Specifically, Object A strikes Object B hard enough to jettison it from the seafloor up to sea level/land, let's say the Pacific coastline. I have a timeframe in mind, density & mass of the two...
  17. sadidrahman20

    Speed of falling object underwater

    Is there any formula for underwater falling sphere which can measure the velocity of that sphere at any time before it reaches its terminal velocity? A sample question is: I dropped a sphere into water with 0m/s initial velocity. what will be the velocity of that sphere after 3s? {the radius and...
  18. J

    SNR for an underwater acoustic signal

    Hi, I'm trying to model the transmission loss and SNR of an acoustic signal underwater. I'm using this expression to modelize the transmitted signal: y = sqrt(P)*exp(1i*2*fr*pi*t)' where P is the transmission power in watts, fr is the transmission frequency and t is the acquisition time. The...
  19. S

    Optimizing Dolphin Tracking: Calculating the Angle for Dart Gun Accuracy

    Homework Statement A scientist investigating the movements of dolphins in the Mediterranean uses a dart gun to shoot small, harmless tracking devices onto the fins of dolphins. When standing on deck, her hand is 1m above the water, and looking along the dart gun she is holding at an angle of...
  20. betamu

    Frequency of Reflected Underwater Sound Wave

    Homework Statement The sound source of a ship’s sonar system operates at a frequency of 18.0 kHz. The speed of sound in water (assumed to be at a uniform 20°C) is 1482 m/s. What is the difference in frequency between the directly radiated waves and the waves reflected from a whale traveling...
  21. S

    Breathing Underwater: A High Schooler's Quest

    So I am in high school, so I am not the smartest. That is why I have came here. I was on Kickstarter and saw a underwater drone and I got to thinking, what if we could breathe underwater. So obviously we can't take oxygen from H2O, so what if I made a giant vape type machine? What happens if you...
  22. James8626

    Calculate Tidal Force on Underwater Artwork Sculpture in Philippines

    Can anyone assist. I'm workingg on a project for the installation of an underwater artwork sculpture. How do I calculate the tidal force on the structure to stop it moving on the seafloor. It's not anchored to the seafloor only sitting on it. Also what safety factor should be built into it for...
  23. C

    Underwater acoustics: transmission loss at long distance

    Hi all, I have some problems to understand how to calculate the transmission loss at long distance, which model do I have to use? I was looking into the energy flux model (Weston model), but I didn't understand at what range I should switch from "mode stripping" to "single mode". I am working...
  24. paulmdrdo

    Sound transmission underwater -- looking for equations TX --> Rx

    Hello! I have a system depicted below. I need to know what is the working equation that governs the transmit and receive power of the transmitter and receiver in the diagram. The transmitted signal is a sound wave and not an RF signal, the transmission is underwater. I would like to know what is...
  25. David Dincer

    Cooling for Underwater Monitor Housing

    Hi, I have an underwater monitor housing made out of carbon fiber and an acryllic Glass on the other side. Over time the monitor heats up. I guess carbon fiber is a bad heat conductor :(. the Acryllic glass is almost 1cm thick. Does anybody have an advice on how to cool something like this...
  26. N

    Buoyancy of a sealed hemisphere underwater

    Homework Statement You have a hemisphere, like half a ping pong ball for example, sitting in a cup under a few centimeters of water. The hemisphere is sealed to the bottom so that no water can get underneath it. What is the buoyant force the hemisphere experiences? Homework Equations P = P0 +...
  27. R

    Underwater breathing apparatus?

    How to make changing depths irrelevant for breathing in a small submarine or other manned underwater vehicle; in terms of the under breathing apparatus or system ?
  28. R

    Can someone explain the vacuum pressure created by water pressure on waders?

    Hi guys! I have question regarding vacuum and underwater pressure if anyone here could help me out with it. I'm not really a physics person (my math skills suck too much, lol), but I do find it very interesting. I recently bought some breathable stockingfoot fly fishing waders and whenever I...
  29. fluidistic

    Surviving a fire by going underwater in the bath with a ball

    I'm wondering whether it's possible to survive most fires by filling the bath with water and a balloon with air (it doesn't matter if it comes from human exhalation), then go underwater and breath through the balloon. When I was a kid I used to breath in a balloon that I would fill with air by...
  30. R

    Pressure a sphere of polycarbonate can withstand underwater?

    Specifically, how deep can an enclosed space of a polycarbonate (I'm thinking about strong plastics) material withstand underwater before cracking and breaking. Say a 2 liter bottle
  31. Planobilly

    Need Ideas for deep underwater LED light

    Hi guys, I am trying to build a underwater camera system with lights. The depth requirement is 1500 feet. I need to view the bottom well enough to understand what conditions exist. I need to know if the bottom is rock or sand or mud. I have solved the camera issue...well I think...lol The...
  32. R

    Underwater Propulsion: Pumping Out Water for Acceleration

    Can water inside a submersible object be pumped outwards to provide an acceleration while underwater?
  33. R

    Optimal Shape for a Submersible Object with 360 Degree Maneuverability

    For a given submersible object that has 360 directional maneuverability, what would be an ideal shape for that object? Sphere? **360 degree directional maneuverability meaning jets strategically placed around the object for propulsion, without rotating the object
  34. H

    Sound underwater distance and decibels

    I was wondering if sound underwater traveled further than sound in air? It seems like it wouldn't do to viscosity. I know that it travels faster however. Lastly, is the online reasoning for why we can't hear sound as well underwater correct: the water vibration bypasses some of the sensory...
  35. Tomimo

    Making bubbles and trying to use Trompe

    Hi, I am trying to create a device that would "simply" make a bubble under the water. What I am aiming for is production of small bubble but continuously and under the water. When I say continuously, it doeant have to be for extended periods of time, could be just for ~2 hours but the longer...
  36. P

    Finding the tension in a rope attached to a gate underwater.

    Homework Statement 2 & 3. The Attempt at a Solution I've worked out: The total force on the gate. I have worked out the centre of pressure which I got a value of 10/3m (from the hinge). For the moment about the hinge I got a value of 981,000Nm using the equation M=FN*X where X is the centre...
  37. T

    Why is it harder to run underwater but easier to lift

    Both involve water resistance, buoyancy, and density of water and air. Therefore, I would expect that the lift up of your foot would be easy but putting your foot down would be the most difficult. Lifting an object is easier bc of buoyancy force. Although, apart the object must be buoyant...
  38. tjvv

    How to detect that my device is underwater?

    Hi, I have a waterproof smartphone with sensors like barometer, gyro, accelerometer, microphone). I want to do an app that 1) detects that the phone is underwater: I though in using some reading from touch panel as water is electro conductive and it may provide me some reading to indicate...
  39. Wanna_be_Feynman

    Distance a bullet will travel while shot underwater

    Homework Statement hey I am trying to work out the problem: If I shoot an ak47 underwater with 7.62x39mm ammunition, how far will the bullet travel before coming to a stop? Homework Equations The equation that I have used to find the drag force is the drag equation: F =1/2 p*A*C_d*v^2...
  40. Alfreds9

    Maximum light intensity underwater during seasons?

    Hi, I was thinking if maximum light intensity underwater during seasons changes somehow. I firstly thought about considering monthly solar irradiance (http://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_INSOL_M) however I thought this would have been biased at certain latitudes due to...
  41. A

    Working out tension of string holding a ball underwater

    I have a physics homework question that i need help with; A submerged ball of negligible mass is attached to the bottom of a swimming pool by two strings as shown. The volume of the ball is 5000cm^3. Calculate the tension in each string. (hint you need to look up the density of water) How do i...
  42. B

    Need to build an underwater housing for camera

    will an aluminum tube 127mm in diameter, 3.5mm wall thickness, enclosed on either end by 12mm thick disks with o-rings be able to with stand 15bar of pressure. Its for an underwater camera housing.
  43. F

    Creating controlled cavitation underwater (bubbles)

    Hello all- First post. I am curious if it is possible to create cavitation underwater with these specific criteria. I am basically using a venturi device that will be pulled underwater in saltwater. Is it possible to get the vapor pressure down low enough to boil water (make bubbles). I have...
  44. NPB777

    Variation of Frequency of sound underwater

    Hello, I am very much interested to how frequency of sound varies in water. Also, how the frequency varies with temperature and depth? What are the different formulas related to this? Secondly, how can we determine the best frequency of operation? I would be very thankful if anyone could answer...
  45. Lee power

    Chemical reaction metal underwater

    Hi guys I was wondering of someone on here could briefly enlighten me on the chemical reactions that would occur with a Teflon Coated high carbon steel hook and a lead sinker while underwater? I am looking into the signals that may or may not be given off by these items both separately and with...
  46. S

    Is sound amplified underwater?

    Hi all, Is sound amplified underwater? My reasoning is if a sound is louder underwater than it is on land, then it has been amplified. Is this correct?
  47. K

    Pressure underwater and equivalent weight

    Hello, I am trying to calculate the equivalent amount of weight that a submarine would be under at 1000m below the sea. Apologies if this isn't that well explained! At 1000m - 101 atmospheres - which is 14.5 psi per atmosphere - so at 1000m it would be 1464.5 psi. Do I then multiple 1464.5 by...
  48. N

    Can a Bullet Break a Bike Chain at 6m Underwater?

    < Mentor Note -- OP has been reminded to use the HH Template and show their work in future posts... > A man fires a bullet into a swimming pool. There is a distance of 6m from the gun to the bottom of the pool. Does the bullet have enough force through the water to break an average bike chain...
  49. Charlie Kay

    How do I calculate the acceleration of gravity underwater?

    Does anyone know a simple formula to calculate the acceleration of gravity underwater?
  50. Charlie Kay

    How can I calculate underwater pressure quickly

    Does anyone know a simple formula to calculate underwater pressure?