Why does water offers less friction?

[Kaustubh sri]

Why do water offers less friction?

My attempt
as water friction is less than air

can anybody tell me that i am right or not

 

[Orodruin]

It should be relatively clear that (liquid) water has higher viscosity than air. Just try to drag your arm through water and then through air. Which offered less resistance?

 

[Kaustubh sri]

Ok then tell me that if someone is swimming at the surface of water he/she get high friction while during inside water it doesn't.Why?

 

[RGEmpress]

I have a certain interest in this as well. I think viscosity is something akin to thickness of a fluid, and from experience, it is a lot easier and faster to move in the air than in the water.

 

[NascentOxygen]

Ok then tell me that if someone is swimming at the surface of water he/she get high friction while during inside water it doesn't.Why?

A submarine uses much less fuel when traveling on the surface of calm water than when fully submerged, for the same speed.

 

[Orodruin]

Friction is not the only force responsible for slowing a swimmer down. This page seems to summarize in a relatively concise manner: http://coachsci.sdsu.edu/swim/bullets/forces4.htm

 

[CWatters]

Google found this on the submarine issue..

http://www.fleetsubmarine.com/phorum/read.php?f=6&i=4&t=2

Re: surface speed vs. submerged speed

A number of factors affect surfaced and submerged speeds. In most WWII era boats, surfaced speed was considerably higher than submerged. In a Gato, about 20~21 knots surfaced, 9 submerged. A lot of this had to do with hull design. The old boats were really surface warships with a limited ability to dive, so they were designed for surfaced efficiency. Once submerged, deck guns, the conning tower fairwater, radio antennas, and any number of projections interfered with the smooth flow of water, slowing the boat.

Late in the war, Germany reversed that concept, designing boats with streamlined hulls for greater efficiency under water. The type XXI u-boats are generally thought of as the first production submarines designed to be faster submerged than on the surface. A second factor in this was adding a lot of cells to the batteries, as battery capacity was a limiting factor in both speed and range. Run at full speed, a submerged fleet sub would run her batteries flat in about an hour.

The design of the screws is also important, but in that case depth is even more important. Cavitation--the swirling stream of bubbles you see in movies--robs efficiency, but as you reach a critical depth the water pressure becomes great enough that cavitation ceases and the screw gets about as close as possible to 100% efficiency. This happens rather abruptly, with the motor/turbine suddenly speeding up without any increase in power setting as cavitation-caused drag ceases.

The same pressure factor also makes the hull more efficient at depth, with the energy that was formerly wasted in creating a wake--which you get, even if you can't see it, to a considerable depth--now available for speed as the water pressure suppresses the wake and forces the water to flow smoothly around the hull. (By now tear-drop or cylindrical in shape.)

The periscope has little to do with speed, as no submarine intentionally travels very fast at periscope depth in order to avoid throwing up a lot of visible spray and possibly giving away her position. In the old boats, the exposed periscope shears certainly created turbulence and robbed speed, of course. In modern boats, everything that sticks up above the fairwater can be fully retracted.

J.T. McDaniel
Webmaster, FleetSubmarine.com
Author of: With Honour in Battle and Bacalao
General Editor: American Submarine War Patrol Reports series

 

[CWatters]

Why do water offers less friction?

My attempt
as water friction is less than air

can anybody tell me that i am right or not

Sometimes water increases friction. Sometimes water reduces friction. It depends on the situation. Can you expand the question?

 

[HallsofIvy]

Why do water offers less friction?

My attempt
as water friction is less than air

can anybody tell me that i am right or not

Water offers less friction than what?

If you are referring to simple motion through water or air, water does NOT "offer less friction".

Perhaps you are referring to "slipping" on a wet surface?

 

[SteamKing]

Why do water offers less friction?

My attempt
as water friction is less than air

If this were true, we'd be flying airplanes underwater.

 

[AlephZero]

Ok then tell me that if someone is swimming at the surface of water he/she get high friction while during inside water it doesn't.Why?

If you are swimming at the surface, you generate waves. Ignoring the "splashing" effect of arms or legs entering or leaving the water, there is a large increase in the resistance force when an object reaches a critical speed which depends mainly on its length, because it is effectively traveling "uphill" trying to climb up the bow wave it generates in front of it. A boat with a high power engine, or a sailing boat in a strong wind, can get "on top of" its bow wave and is then effectively traveling down hill with the front of the hull completely out of the water, until it has to slow down.

Apparently ducklings can do this to escape from predators quickly, even if human swimmers can't. http://jeb.biologists.org/content/198/7/1567.full.pdf

 

[RGEmpress]

If you are swimming at the surface, you generate waves. Ignoring the "splashing" effect of arms or legs entering or leaving the water, there is a large increase in the resistance force when an object reaches a critical speed which depends mainly on its length, because it is effectively traveling "uphill" trying to climb up the bow wave it generates in front of it. A boat with a high power engine, or a sailing boat in a strong wind, can get "on top of" its bow wave and is then effectively traveling down hill with the front of the hull completely out of the water, until it has to slow down.

Apparently ducklings can do this to escape from predators quickly, even if human swimmers can't. http://jeb.biologists.org/content/198/7/1567.full.pdf

Loons ((the state birds of Minnesota (US)) are really good at that! I don't know what their favorite fish is, (too personal to ask a Loon) - read my intro for reference to that one! - but I think this wave interference thing is what Kaustubh sri was speaking of. :-)

 

[Kaustubh sri]

Thanx to every one helping me in the que.

 

[CWatters]

What was the question?

 

[vela]

Why do water offers less friction?

My attempt
as water friction is less than air

can anybody tell me that i am right or not

If I were grading this question, you'd get a 0 for that answer. You're essentially saying "water has less friction [than air] because it has less friction than air." It's not an explanation; you're just repeating the question as the answer.

 

[Student100]

Should the term friction even be used in the context of the discussion?

 

[Kaustubh sri]

Dear @vela i was only asking that i am right or not

 

[vela]

I know. I'm pointing out that you're not answering the question. It's like if you were asked why the sky is blue, and you answer, "because it's blue!" It's not an explanation. You're just merely restating the question in statement form.

Q: Why is there less friction?
A: Because there's less friction.

Can you not see that?

 

[Kaustubh sri]

I know. I'm pointing out that you're not answering the question. It's like if you were asked why the sky is blue, and you answer, "because it's blue!" It's not an explanation. You're just merely restating the question in statement form.

Q: Why is there less friction?
A: Because there's less friction.

Can you not see that?

Sorry if it hurts you but i didn't mean that you thought about

 

[vela]

I'm simply pointing out that you're making a very common mistake students make when they think they're answering a question but they're in fact not doing so. I assumed you were here to learn, but apparently not. If you don't care, it's no skin off my back.

 

[Kaustubh sri]

Ok ok thanks if you meant it for my mistake