Wikipedia:Reference desk/Archives/Science/2018 February 8

In principle, would an Amtrak Superliner be able to operate into northern Mexico, if desired? Or would the loading gauge preclude this (as it does on some lines in the eastern USA)? 2601:646:8E01:7E0B:61B1:2817:FCB1:9B27 (talk) 03:35, 8 February 2018 (UTC)[reply]

Depends on the wagon construction. The Bombardier–Alstom HHP-8 Superliners for example look surprisingly low for their two levels. --Kharon (talk) 12:06, 8 February 2018 (UTC)[reply]

Anyone have hard numbers on this? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 12:59, 9 February 2018 (UTC)[reply]

Hello! Somebody? Anybody? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 10:23, 12 February 2018 (UTC)[reply]

A report in the London Daily Telegraph of 31 January [1] says:

Whales are known for their impressive communications skills which allow pods to "talk" to each other through complex clicks and singing, even when they are 100 miles apart.

Later it says:

Whales also use their tails and fins to make loud slapping noises on the surface of the water to communicate with each other non-verbally.

The sound can be heard for hundreds of feet below the surface and may be a warning sign to other members of the pod.

What is the maximum distance sound can travel through different propagating mediums? (I know that it can't travel through a vacuum at all). It appears that sonar only travels a few miles. 92.19.173.221 (talk) 11:05, 8 February 2018 (UTC)[reply]

Whale vocalization says

Prior to the introduction of human noise production, Clark says the noises may have travelled right from one side of an ocean to the other, agreeing with a thirty-year-old concept blaming large-scale shipping.

And it still travels for thousands of km. From the research of Dr Christopher Clark of Cornell. ^[1]

I had a brief look at Bioacoustics and Underwater acoustics - you might get more info from their reading lists. Carbon Caryatid (talk) 11:28, 8 February 2018 (UTC)[reply]

You may find SOFAR channel interesting.

Mikenorton (talk) 11:30, 8 February 2018 (UTC)[reply]

The answer depends completely on signal strength and sensor sensitivity. Sound travels much faster in water (~1500 m/s) compared to air (~330 m/s). Additionally air has a much higher dampening effect on soundwaves compared to water because air is compressable gas and thus works like a weak spring while water is a not compressable solid fluid that works like a very hard spring which helps greatly to carry a wave on long distances. Thousands of km should be possible with very sensitive sensors/ears. In comparrison seismic waves can be detected around the world with no problem but these are usually very strong waves and very sensitive sensors (Seismometers) --Kharon (talk) 11:52, 8 February 2018 (UTC)[reply]

"The answer depends completely on signal strength and sensor sensitivity."

No, it absolutely doesn't. That would be the case for a consistent isotropic medium. Seawater, for the purposes of sound, is anything but. In particular there are layers within the sea of differing salinity and temperature (see thermocline). In the right conditions, this can give rise to a waveguide effect where sound propagation can be far further than for the expected simple case. Submarines are well aware of this, it's likely that whales are too. Andy Dingley (talk) 13:11, 8 February 2018 (UTC)[reply]

The question was "What is the maximum distance sound can travel". So you can negate unfavorable conditions and assume them perfectly supportive. No thermal layers, no difference in salt containment, no interference from wave reflections from geologic "landmarks", no gray- or white noise - not even pink noise. --Kharon (talk) 23:46, 8 February 2018 (UTC)[reply]

But waveguide effects between layers are favourable conditions, and dramatically increase the range. Andy Dingley (talk) 10:57, 9 February 2018 (UTC)[reply]

• All of the above, plus differences based on the frequency of the sound signal. Different SONARs operate at different frequencies, from ultrasonic down to infrasonic. Whales also use a variety of frequencies. The differences cah be dramatic, especially when different water layers form a waveguide that enhances some particular frequency range. -Arch dude (talk) 03:29, 9 February 2018 (UTC)[reply]
• The Heard Island Feasibility Test in 1991 proved some remarkable long-range sound transmission, with a source near Heard Island in the southern Indian Ocean being detected in the North Atlantic and on the US Pacific coast. Mikenorton (talk) 10:35, 9 February 2018 (UTC)[reply]