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Just a random question out of interest.

When you hear an explosion, e.g. a firework, firecrackers etc, from far awa how does the sound reach our ears so quickly?

The speed of sound in air is like 300m per second, and if a firework 2 km diagonally away from me in the sky explodes, then mathematically it should take 2000m/300mps ~ 6-7 seconds to travel to our ears..... But in reality we all hear it right away. Whats going on?

Do all sounds I hear from afar, like planes, are sounds created seconds ago in 'the past' or do I hear it closely to when it was formed

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    $\begingroup$ You don't hear it right away. You just have no direct experience with fireworks so are completely unable to judge their size or distance when they are up in the sky. Have someone hit a shovel on concrete from even just 1km away. You will clearly experience the delay. I noticed this when I was ten years old outside playing during the winter and people were trying to break through ice on their driveways. And personally, I do hear a delay. You have to listen and watch carefully because if all you ever see and hear are fireworks from far away your brain tunes it out as the way fireworks should be. $\endgroup$
    – DKNguyen
    Jan 2 at 5:01
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    $\begingroup$ for reference, fireworks are usually sent less than 100m in the sky. But they definitely obey the speed of sound $\endgroup$
    – Señor O
    Jan 2 at 6:14
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    $\begingroup$ It's possible that the sound from a firework reached you around the same time another firework went off. Also, you can tell that the sound from a plane flying high overhead appears to come from far behind it. $\endgroup$
    – Puk
    Jan 2 at 6:26
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    $\begingroup$ if I had to choose personal experience or physics (done right), I'd always rely on physics first. Never watched fireworks from long distance and short distance? Time delay is proportional to distance as $L/a$: you could easily make mistakes in your estimation of distance $L$, while you can take $a=300 \, m/s$ as a good estimate of speed of sound in air within 20% error $\endgroup$
    – basics
    Jan 2 at 9:25

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The short answer is yes, you are hearing sound created in the past. This delay in the sound is very noticeable if you watch a thunderstorm that is some kilometers away. You see the lightning flash (almost) instantly and then you hear the corresponding thunder clap some seconds later.

Over great distances, even light is significantly delayed. For example if you observed an astronomical event such as a supernova, when you see the flash might be thousands or millions of years after the time the explosion actually happened.

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we do not hear the sound all at the same time. take the following case:

You are 300 meters away from a bomb. Friend #1 is 600 meters away and friend #2 is 900 meters away.

The bomb goes off and you see the flash. One second later, you hear the bomb. Two seconds later, friend #1 hears it. Three seconds later, friend #2 hears it.

Now we bunch you all together. You are 300 meters from the bomb, friend #1 is 303 meters away, and friend #2 is 306 meters away. The bomb goes off and all three of you see the flash. You hear the bomb one second later, friend #1 hears it 1.01 seconds later, and friend #2 hears it 1.02 seconds later. But since your ears cannot be calibrated accurately to one another, all 3 of you report hearing the bomb at about the same time.

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