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. M

    Underwater low pressure water hydraulics

    I'm after a dc waterproof water pump that can handle at least 60 feet of water, around 10 gallons a minute flow rate at 50 psi. finding this combination seems to be a real problem.any ideas?
  2. K

    Can You Pop an Underwater Air Bubble by Poking It?

    If you poke at a soap bubble floating in air it pops. Can you make an underwater air bubble pop when you poke at it? I say no, my wife thinks you can. What say you? And why?
  3. logickills

    Building Underwater Coil Gun/Mass Driver: Considerations & Questions

    I have a question regarding the propagation of ferromagnetic materials via a coil gun or mass driver in an under water environment. Would the surrounding water effect the firing and or power of the shot. I know the water resistance is one thing to overcome. I was counting on using this more...
  4. W

    Understanding Submerged vs Underwater Objects: A Quiz and Explanation

    i understand that an object with smaller density than water will float on water with the same density, it will be submerged and "suspended" in the middle of the water my question is in the case of an object being denser than water, it will sink and finally touches the ground (underwater)...
  5. T

    Volume of block given underwater and land weight

    Homework Statement A block of metal weighs 9N in air and 7N in water. What is volume of block? correct answer: 200cm^3 Homework Equations w=mg d=m/v The Attempt at a Solution I figured out that it has mass of 0.9kg on land...which may or may not be helpful.
  6. T

    What is the weight of a hollow sphere underwater?

    Homework Statement A hollow sphere has average density of 3 g/cm^3 and a mass of 120g. What will the sphere weight under water? correct answer: 0.8 Homework Equations d=m/v w=mg The Attempt at a Solution I converted 120g into kg and then used w=mg to find weight on...
  7. H

    How do you seal a rotor underwater?

    Lets say I will be operating a generator underwater in a "box" sitting on the river floor. Turbine blades will be spinning a rotor attached to said generator, and obviously the turbine blades are exposed to the water and the generator is sealed in the box. I'm having trouble identifying what...
  8. C

    Underwater Pressure: 9.42 ATM, Find Vessel's Depth

    Homework Statement The pressure exerted on an underwater vessel is 9.42 ATM. If the vessel is in fresh water, to what depth has the vessel descended? 2. Formula P=Po + pgh It is fresh water so p=1000 kg/m^3
  9. S

    Underwater Tension Homework: Calculate Force at Point x

    Homework Statement http://img208.imageshack.us/img208/5158/29172992.jpg So we have some kind of pole floating in water. Area = A. Density = rho. At the bottom we have a point weight M. We want to calculate the normal tension inside the pole $\sigma$ at a position x. I have the...
  10. Ivan Seeking

    Is the underwater volcano near Tonga as dangerous as Surtsey?

    Video at the link. http://www.timesonline.co.uk/tol/news/environment/article5936330.ece
  11. W

    Buoyancy (Weight of a barbell underwater)

    A bodybuilder is holding a 20-kg steel barbell above her head. How much force would she have to exert if the barbell were lifted underwater?Fb= Density x Volume x Gravity Density= mass/volume 7860= 20/ V V= .00254 m^3 Fb= 1000 x .00245 x 9.81 Fb= 24.9174 N
  12. P

    Underwater Lightbulb Optical Illusion - Reflection/Refraction of Light

    Homework Statement "Provide a true explanation for what you see as you look at a lightbulb underwater" (See the attached Image) What you see: Out of water -> white opaque light bulb Underwater -> clear outside, opaque white inside Homework Equations N/A The Attempt at a...
  13. K

    Brushless DC Motors suitable for Underwater?

    Hi people, im new to this forum. I'm currently working on a underwater ROV for my school project. We did a experiment recently on the performance of our ROV. We met up with some problems on the motor & the propeller for the thrusting. The motor stalls just after 5secs. So I am thinking is...
  14. U

    Compression of a sphere underwater

    Homework Statement A solid metal sphere of volume 1.05 m^3 is lowered to a depth in the ocean where the water pressure is equal to 1.38 x 10^7 N/m^2. The bulk modulus of the metal from which the sphere is made is 9.9 X 10^9 N/m^2 Given: The atmosphereic pressure is 1.013 10^5 Pa. What is...
  15. S

    Why Does an Object Appear Larger Underwater?

    Hey I've wanted to know why does the image of an object, which was put in water, seems to be larger than the real object, for a person, who sees it from outside the water. Thanks :smile:
  16. F

    Work done lifting an object underwater

    hi! I have a question regarding work done lifting an object vertically upwards, under water. I am aware that work is done against hydrostatic pressure (which varies depending on a depth h from the surface), and that density of the fluid and the object may have a role in the calculation of...
  17. G

    Total internal reflection, underwater light

    [Solved] Total internal reflection, underwater light? Homework Statement A point source of light is at the bottom of a koi pond, at a depth of 0.525 meters. What is the radius of the circle of light formed on the water's surface? Take the index of refraction of water to be 1.33. Hint: Some of...
  18. D

    Crush pressure on an underwater vacuum tube

    So... let's say I wanted to drop a pipe on the ocean floor with a 6" inner diameter... which has a pretty strong vacuum in it... what general size/material do you suppose that would require... assume it is miles long. I guess you could keep the vacuum pipe inside of another pipe that does not...
  19. S

    Forcing water from a pipe underwater

    Hi I have a problem beyond my scope. I am not a lerned physics chap so please, any answers would be great if kept simple :) I have a pipe containing 300 litres of water. The pipe is 346mm diameter and 1 meter long. The top edge of the pipe is 1200mm under the sea. The pipe lies...
  20. D

    How to Calculate the Work Done When Pushing a Ball Underwater?

    Homework Statement A ball of which radius is 15 inches is put into water and it sinks 2.5 inches. How much is the work done when it's pushed halfway under water? Homework Equations Air pressure doesn't have to be taken into account (not sure about that but that one I can do myself anyways)...
  21. S

    How can I graph the color spectrum underwater based on my scuba diving data?

    hi guys I am new here. for my final year physics assignment i am testing how colors are absorbed under water at different depths. i am planning to go scuba diving and take photos of a color spectrum at certain depths as was wondering if anyone here new much about this and would be able to...
  22. R

    Kinematics: Average Deceleration Underwater

    [SOLVED] Kinematics: Average Deceleration Underwater Hello! First poster here. :cool: Here is a tough question from my online HW: Homework Statement A person jumps off a diving board 5.0 m above the water's surface into a deep pool. The person’s downward motion stops 1.6 m below the...
  23. P

    The mysterious underwater pyramid at Yonaguni in Japan

    This has intrigued me, mainly because a lot of the scientists that go and see it for themselves change their mind and end up thinking that it is not a natural formation. It is an absolutely huge stone monument off the coast of Japan, and it has right angle sides, parrallel ledges, steps, and...
  24. S

    Comparison of sound waves in air and underwater

    [SOLVED] Comparison of sound waves in air and underwater Homework Statement In air, the human ear is most sensitive to sound waves of 3300Hz. The auditory canal is part of the human ear. It is a tube of length 0.025m, i.e. 1/4 the wavelength of sound with frequency 3300Hz. When under...
  25. K

    Measuring underwater electricity

    Suppose I connect 2 9v batteries (for example) in series with a fish tank (30mm x 30mm x 20mm) containing water and an ammeter, is the current registered the same as the current in the water? I should think so but I am not sure. The copper wires-cum-electrode being positioned at either ends...
  26. R

    Power Required to Pump Air Underwater: Calculate & Analyze Metric Results

    Would be grateful for a formula for the power required (theoretically) to move air down to a specified depth underwater. Metric if possible please. My calculations seem an order of magnitude too low.
  27. K

    Pill bug Selective Breeding for breathing underwater

    http://en.wikipedia.org/wiki/Armadillidium_vulgare they are terrestrial crustaceans, but they have gills, i know this might be kind of a stupid topic but could it be practical and it be possible to select the bugs with better gills then the rest, have them breed with each other, so on and so...
  28. F

    Fluid Dynamics: Pressure / Opening a hatch underwater

    Let's say that you're deep under the surface of the water in a submarine type thing. There is a hatch on the top. Let's say that the absolute pressure on the top of the hatch was calculated to be 2 atm. Inside the vessel, the pressure is only 1 atm. Someone is inside the vessel and...
  29. D

    A question of lifting bodies underwater

    If I have two rubber coated kevlar balls, one is filled with air and the other has a gas like helium in it, if submerged underwater, would the ball with helium be harder to keep underwater than the air filled ball would be, or would they be equal in their buoyancy? Also is helium easier to...
  30. 2

    How Can I Calculate the Weight and Compression of a Submerged Coffee Can?

    Math isn't a strong point of mine, and hope someone could give me a valid response to this. I'm still working on underwater physics, and have two questions. First, if I had a 34 oz coffee can that I want to submerge below water to a depth of 8 feet, how many pounds would it take to get the can...
  31. V

    Underwater Pressure sunken ocean liner

    Homework Statement While exploring a sunken ocean liner, the principal research found the absolute pressure on the robot observation submarine at the level of the ship to be 413 atmospheres. The density of the surrounding saltwater was 1025kg/m^3. Calculate the gauge pressure on the sunken...
  32. 2

    Pressure on an item underwater

    When an item is submerged underwater, I believe that pressure from the surrounding water is equal in pressure around the item except from beneath, is this correct?
  33. S

    Why Can't I Swim Underwater Without Closing My Nose?

    I always used to swim underwater but one day, I saw someone standing by their hands underwater, so I closed my nose by my hands and copied him. Since then, I can only swim underwater closing my nose w/ my hands, but then again, I need both of my hands to swim. So, I actually can't swim...
  34. J

    Which Brick Is Harder to Keep in Place: Brick A or B?

    Hello, There are two bricks underwater. Brick A is closer to the surface and Brick B is further down below. Which Brick would be hardest to keep in place? I said Brick B becuase there is more pressure (H20) on it forcing it down + gravity. Brick A just has gravity and a little bit...
  35. T

    Explore the Mystery of the Underwater Mountain & Penguinos

    will someone who has google Earth please go to 1 deg 55'24.90"N 157 deg 21'52.47"W at an altitude around 100 miles Do you see an underwater mountain the exact same size and shape as the island next to it? the two foot print shapes could be where god stood when he created the earth, but...
  36. F

    Animal that can swim underwater, run on land, and fly in the air?

    What's an animal that can swim underwater, run on land, and fly in the air? Mythological or not. Just curious :smile:
  37. wolram

    Malta's Underwater "Cart Tracks": Rewriting Prehistory?

    Andre, mentioned floods in another thread, my interest has been kindled by a program on tv about Malta and under water ,"cart tracks", that may date human civilization 1000s of years older than is previously thought, giving some weight to a massive flood event in pre history, what are...
  38. U

    Why Does a Marble Fall Faster in a Pool Than in a Narrow Tube?

    Can anyone give me an explanation of why a marble dropped into a swimming pool will fall faster than if you drop a marble into a water filled tube with a diameter only slightly larger than the marble itself (presume it doesn't touch the walls of the tube). It's something to do with how quickly...
  39. J

    Fantastic updates on Cuba underwater structures

    "...It is true that down there at heart of the sea, are structures that sometimes have dimensions of several hundreds meters that are unusual, for which we we do not have a simple, direct explanation... " "...rocks appear. Some of them are not typical of Cuba. This leads one to think of two...
  40. W

    What are these underwater structures in Japan and Scotland?

    http://www.cyberspaceorbit.com/phikent/japan/japan2.html http://www.aliensthetruth.com/Worldmyst.php?ID=27 http://www.lightnet.co.uk/informer/civilisations/japan.htm Are these really pyramids underwater? What do you think
  41. S

    Does the Spectrum Change Underwater When Exposed to Light?

    Hey this may be a stupid question but here goes... If you're underwater, say in a pool or something, and someone shines a light into the water will you see a color change? Why or why not?
  42. V

    Calculate Pressure Underwater for a 1cm3 Air Bubble at 291m

    I guess my real question is: does the depth of the water make any difference or do i assume it's constant pressure? If i can't make that assumption, how do i calculate the pressure the water has on this? The obvious answer is that if it's to the nearest tenth of a cm3, it's still coming out...
  43. S

    Book on transducers in marine or underwater acoustics

    Hey I'm hoping there are some people involved in marine acoustics here :) I was hoping that someone here could maybe recommend some good books or sites that exaplain the use of transducers in Marine Acousitcs. I just need to have an idea of what sort of transducer I'm looking at. The carrier...
  44. S

    Calculating Force of 29.9kg Barbell Underwater

    -----A bodybuilder is holding a 29.9kg steel barbell above her head. How much force would she have to exert if the barbell were lifted underwater?---- Ok...I'm really not sure of this one. I thought maybe the answer was the weight of the barbell (mg) plus the atmospheric pressure at sea...
  45. P

    Underwater upthrust problem

    would there be an upthrust or not if a perfectly smooth object was on a perfectly smooth ocean floor? I expect that since there is no water beneath the object there is no pressure to provide an upthrust, there would only be pressure above the object creating a downward force!?
  46. T

    Why do we need to wear goggles underwater to see straight

    I have a question i know it has something to do with refraction but uh... why do we need to wear goggles underwater to see straight>??
  47. Ivan Seeking

    Sea-gypsy Children : Human underwater sight secrets revealed

    "Sea-gypsy Children": Human underwater sight secrets revealed http://www.sciencenews.org/articles/20030517/fob4.asp
  48. I

    Troubles with Swimming Underwater: Tips for Staying Submerged

    When I go swimming (or rather walk in the water; I can't swim but I can pretend :redface: ), I like to try to swim under water and when I try, I can't. Why? Because I only stay under for a few seconds and float right back up again. I took a swimming class once, and the teacher couldn't figure...
  49. V

    Laser in underwater lidar application?

    what can be the output beam diameter for microchip PULSED laser in underwater lidar application?
  50. Another God

    Fluid Dynamics: Air Rising from Water Questions

    I'm curious about some fluid dynamics stuff, and my first series of questions I have are to do with how air rises out of water... Having done some scuba diving, I know that divers use bladders to achieve neutral bouyancy and positive bouyancy so as to hover or rise through the water. Now...
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