Here I thought I knew some physics

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ghettomaster

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#283892 18-Mar-2021 10:35

Hi,

We live in Pinehaven, and often hear the civil defence alarm going off down at the Silverstream fire station.

Yesterday, I was in the phone to my wife who was down in Silverstream while I was at home, and I heard the siren through the phone a good second or two before I heard it outside. It was certainly long enough for me to hear it on the phone and wonder why I couldn’t hear it outside.

How does that work? Is it because the higher frequencies used by the phones travels faster than the frequenc... argh! As I type that I’m suddenly thinking about light vs sound and remembering of course that’s it.

Pretty impressive on the phone networks part though as we would have been on different cell towers.

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#2676401 18-Mar-2021 10:40

Radio waves for the cell network travel a lot faster than sound, which is about 330 m/s. So very roughly takes about 3 seconds for sound to travel 1km. There will be some delay in cell network, but if you are more than say 1/2km away, you will hear it through the phone first.

Batman

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#2676407 18-Mar-2021 10:48

Do phone networks get lagging

SaltyNZ

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2degrees

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#2676416 18-Mar-2021 11:02

Batman: Do phone networks get lagging

There is a short lag built-in because the voice coders chop the speech up into 20ms chunks, so that's the minimum possible latency. Other than that I wouldn't expect more than on the order of another 10-20ms of latency added as it passes through the network.

But that's probably still supersonic over more than a couple of km. :-)

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Oblivian

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#2676423 18-Mar-2021 11:13

That's just the fire siren BTW. Silverstream is Volly.

That said, sure, CD can ask they sound them as part of any sort of wider emergency. But primarily the stations use.

Wait till someone complains and they will follow down here. No sounding after 9PM to 6AM anymore. Just pager, and if noone responds in 3mins it will sound.

1101

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#2676424 18-Mar-2021 11:14

Nothing to do with frequency

sound : travels at the speed of sound

From your basic physics you will know Maxwells equations :)
radio waves : travel at the speed of light . Thats just a tad faster .
Add some slight lag as is gets processed through the cellphone systems . Add some slight lag as its not in a vacuum .

Because the earth is Flat the difference isnt what you would you were taught at school .
My tinfoil hat does cause some distortion in spacetime as i do my best to avoid all microwaves , so i factor that in.

frankv

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#2676425 18-Mar-2021 11:16

Whether over the cellular net or landline, signals in the phone system are electrical (or optical) and travel at some large fraction of the speed of light. For air, 0.998C, so 3 microseconds/km. I don't know the exact figures for copper, but way back in the CSMA/CD days Ethernet expected propagation at 0.7C. In fibre it's about the same at 0.69C, so maybe 4 microseconds/km for landlines. Sound in air is about 3 seconds/km, i.e. about a million times slower. There will be some delay in switching and so on in the network, and the signal may go by a very indirect path, but the delay will only be noticeable to people if it goes to a geostationary satellite and back (72,000 km round-trip).

Interestingly? when we use MS Teams, there is a half second or so delay between my coworker at the next desk saying something and me hearing it via Teams. It's very off-putting. I wish I could stop his voice coming to me in the call.

Oblivian

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#2676430 18-Mar-2021 11:22

Talking to Auckland via sat/microwave back in the day. Eh gads that was horrid.

And yes. Teams processing when housed enmasse is ick. I got a new headset to block that, but its weird not hearing your own voice other than through your jaw too

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rogercruse

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#2676432 18-Mar-2021 11:29

ghettomaster: ... my wife who was down in Silverstream while I was at home...

And you believe her?

ghettomaster

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#2676479 18-Mar-2021 13:18

rogercruse:
ghettomaster: ... my wife who was down in Silverstream while I was at home...

And you believe her?

Now that you mention it, I thought the McDonald’s drive through speaker in the background was the giveaway but I guess there’s more than one of those around these days...

So confession time. Physics fascinated me which makes me really regret dropping it about five minutes in, or around about concave mirrors.

I would have thought radio waves would be slower than light though. There’s something I’ve learnt.

ghettomaster

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#2676483 18-Mar-2021 13:23

Also what does silverstream is volly mean?

Ge0rge

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#2676484 18-Mar-2021 13:23

ghettomaster: Ok more questions.

What does Silverstream is Volly mean?

The station is manned by volunteers - it doesn't have a crew on station at all times.

Hence the siren to notify them that there is a call and to rush to the station.

RunningMan

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#2676490 18-Mar-2021 13:32

ghettomaster: I would have thought radio waves would be slower than light though. There’s something I’ve learnt.

They are slower than light, but still many orders of magnitude faster than sound.

wellygary

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#2676495 18-Mar-2021 14:05

ghettomaster: Hi,

We live in Pinehaven, and often hear the civil defence alarm going off down at the Silverstream fire station.

Yesterday, I was in the phone to my wife who was down in Silverstream while I was at home, and I heard the siren through the phone a good second or two before I heard it outside. It was certainly long enough for me to hear it on the phone and wonder why I couldn’t hear it outside.

How does that work? Is it because the higher frequencies used by the phones travels faster than the frequenc... argh! As I type that I’m suddenly thinking about light vs sound and remembering of course that’s it.

As others have said its due to the speed of Electromagnetic waves (phone frequencies and fibre and wire transmission) vs sound waves (air compression)

This is basically a slightly different example of the classic "seeing lightning and then waiting to hear thunder"

frankv

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#2676496 18-Mar-2021 14:07

ghettomaster: I would have thought radio waves would be slower than light though. There’s something I’ve learnt.

All electromagnetic waves (radio, light, X-rays) travel the same speed in a vacuum. In other media (air, water, glass) waves travel at different speeds depending on their frequency. Red light (lower frequency) travels faster than blue through glass. So I guess radio waves (even lower frequencies) travel *slightly* *faster* than light through air or other media.

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#2676515 18-Mar-2021 15:04

RunningMan:
ghettomaster: I would have thought radio waves would be slower than light though. There’s something I’ve learnt.

They are slower than light, but still many orders of magnitude faster than sound.

Umm... I thought it's the same speed as light

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