Why is there a delay in hearing sound after seeing an event?

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Discussion Overview

The discussion revolves around the delay in hearing sound after observing an event, specifically the sound of a skier landing on water. Participants explore the reasons behind the perceived delay, considering factors such as distance, speed of sound, and environmental conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes the observed delay of about 3 seconds between seeing the skier land and hearing the sound of the skis hitting the water, questioning if this is reasonable given the distance.
  • Another participant provides the speed of sound as approximately 340 m/s and asks for the distance to calculate the time it would take for sound to travel that distance.
  • A participant calculates the time for sound to travel 80 meters, estimating it to be around 0.24 seconds, and contrasts this with the negligible time for light to travel the same distance.
  • One participant suggests that the delay might be due to an echo, while another questions why the initial splash was not heard.
  • Another theory proposed is that the sound heard might not be from the ski landing but rather from the boat's rope regaining tension after the skier lands.
  • A participant discusses the influence of temperature on the speed of sound and introduces the concept of refraction, explaining how environmental conditions around a lake could affect sound propagation.
  • One participant mentions standing on a jetty with a small hill behind them, suggesting that terrain could also impact sound travel.

Areas of Agreement / Disagreement

Participants express various theories regarding the delay in hearing sound, with no consensus reached on a single explanation. Multiple competing views remain, including considerations of distance, environmental factors, and potential misattribution of sounds.

Contextual Notes

Participants reference calculations based on basic physics principles, but there are uncertainties regarding the accuracy of these calculations and the assumptions made about sound propagation in different conditions.

MrPickle
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I was at tattershall lakes the other day and a skier went over a jump, about 3 seconds later after he landed you'd hear the slap of his skis hitting the water.

I want to know why? I know that light travels faster than sound, but we wasn't very far away, not far enough for it to make that big-a difference - at least, I don't think so.

Sorry if this is a stupid question :3
 
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How far away was he? Sound travels about 340 m/s--about a mile every 5 seconds.
 
We was about 80m away from where he was landing. I guess I can try and work out how long it'd take for the sound to reach me using my GCSE physics :P

D = S/T? So T = D/S? So it'd take about ~0.24 seconds for the sound to reach me?
and it'd take ~2.7 x 10^-7 for the light to reach me :3 That's not 3 seconds difference?

I'm probably wrong with that, I was just using a formula from class.
 
Your calculations look OK to me. Perhaps you were hearing an echo.
 
Doc Al said:
Your calculations look OK to me. Perhaps you were hearing an echo.

Why would I not hear the initial splash?
 
Beats me.
 
The other possibility is that you are hearing something other than the ski landing, and incorrectly attributing it to the ski slapping the water.

For example a ski-jumper will normally land with the rope slack, but within a few seconds the boat must take up the slack and resume towing the skier before he sinks. You might for example be hearing the sound of the rope slapping as it regains tension.
 
The speed of sound in air depends on the temperature. The 331 m/s is for a temperature of 0 degrees C. The formula to adjust for temperature is V = 331.4m/s+0.61m(s.˚c)t.
So that will likely make your time even shorter.

However when a sound wave passes from one medium into another of different density, its speed is changed. It can bend the direction of the wave and is called refraction. Around a lake you often get a difference in temperature between the water and land. The water takes longer to heat up in the day but also cools slower at night. Also while heating land the air next to the surface heats first and is warmer than air at higher levels, which bends the sound wave up. At night the wave is bent downward and you can often hear people out in the middle of the lake or on the opposite shore as if they beside you.

The terrain where you are at makes a difference too, but it is possible that the front of the sound wave was bent and went overtop of you
 
I was standing on the jetty, and behind me was a small hill.

uart's theory sounds reasonable, I wouldn't be surprised if it was that although, when I was knee boarding I got quiet a lot of slack at one point but I didn't here a crack when the rope was pulled tight again.
 

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