Energy transference and existence

[Half-Dead]

Hi guys, I have this question about energy that I sometimes think about and I thought a good way to get some sort of answer is to visit a forum dedicated to science so here I am. My question might sound a little daft so here it is. I'm probably alone in thinking this haha!

What happens to sound energy? They say energy can't be destroyed and can only change from 1 form to another.... like a light bulb changes electrical energy into heat etc. However, what happens if we listen to music? To my way of thinking our stereo system converts electrical energy to sound (and a bit of heat) but where does the sound energy go after the song is finished?  does it just exist somewhere but in what form? if it can't just die or be destroyed then it has to exist somewhere. 

Thanks

[iNow]

A few immediate thoughts. There is heat in the speaker wires that will radiate until cooled. This will warm the surrounding environment. 

Similarly, the sound waves leaving the speaker compress and expand the air it travels through. They bounces off walls and chairs and tables and any other obstacles in their way. Those obstacles will flex gently and themselves warm up slightly upon being struck by the sound. 

Someone else here may have a better answer to offer. Those are the two which came immediately to mind for me. 

Edited February 16, 2020 by iNow

[studiot]

Good afternoon and welcome.

Have I the pleasure of addressing the dead half or the live half?

 

As regards your very reasonable question, let us start with a few facts and figures.

First and foremost.
There is not a lot of energy in the sound from yoiur hifi.

Let us say you have a big hifi with two 100 watt channels running at 75% power on the dial.

So your amp is outputting 150 watts electrical.

But loadspeakers are notoriously inefficient.
Particularly bass speakers  which can be only 1 % efficient.
Even the best speakers will not exceed 30%.

So this brings down the sound power output to somewhere between 1.5 and 50 watts.

Once this sound is in the air it impinges upon surfaces such as doors, windows, curtains, upholstery and so on.
All of these materials can move flex, wave, twist and so on.
Some more than others.
 

The sound energy is thus converted to mechanical energy of these actions.
In turn this flexing etc warms up the object and so the energy is turned into heat.

Heat is the final destination of all sequences of energy conversion.

 

Does this answer your question?

 

[Half-Dead]

On 2/16/2020 at 1:40 PM, studiot said:

Good afternoon and welcome.

Have I the pleasure of addressing the dead half or the live half?

 

As regards your very reasonable question, let us start with a few facts and figures.

First and foremost.
There is not a lot of energy in the sound from yoiur hifi.

Let us say you have a big hifi with two 100 watt channels running at 75% power on the dial.

So your amp is outputting 150 watts electrical.

But loadspeakers are notoriously inefficient.
Particularly bass speakers  which can be only 1 % efficient.
Even the best speakers will not exceed 30%.

So this brings down the sound power output to somewhere between 1.5 and 50 watts.

Once this sound is in the air it impinges upon surfaces such as doors, windows, curtains, upholstery and so on.
All of these materials can move flex, wave, twist and so on.
Some more than others.
 

The sound energy is thus converted to mechanical energy of these actions.
In turn this flexing etc warms up the object and so the energy is turned into heat.

Heat is the final destination of all sequences of energy conversion.

 

Does this answer your question?

 

I think you're talking to the dead half today haha! 
Thanks for your answer. It answers my question since it provides me with ideas that hadn't entered my head. I never would have thought about the tiny movement of walls/doors etc. I assume the heat energy created from the moving windows/walls etc just goes into the atmosphere and then exists... am i right?

Thanks

On 2/16/2020 at 1:25 PM, iNow said:

A few immediate thoughts. There is heat in the speaker wires that will radiate until cooled. This will warm the surrounding environment. 

Similarly, the sound waves leaving the speaker compress and expand the air it travels through. They bounces off walls and chairs and tables and any other obstacles in their way. Those obstacles will flex gently and themselves warm up slightly upon being struck by the sound. 

Someone else here may have a better answer to offer. Those are the two which came immediately to mind for me. 

Thanks. This indeed does answer my question.

[studiot]

14 hours ago, Half-Dead said:

I assume the heat energy created from the moving windows/walls etc just goes into the atmosphere and then exists... am i right?

Not really.

The sound energy starts off in the atmosphere as mechanical (pressure wave) energy.

The fluctuating pressures are applied mechanically to all surfaces, causing transfer of mechanical energy to the objects with these surfaces.

The mechanical surface energy is then converted within the body of the object to heat energy by internal processes, as the energy spreads theought the body. In the process the body is warmed the body ever so slightly.
The slightly warmed body will then transfer a small proportion of this heat back to the atmosphere.
This amount is a very small percentage of a very small number.

Note that 'soft' objects absorb more sound than hard ones.

[Half-Dead]

2 hours ago, studiot said:

Not really.

The sound energy starts off in the atmosphere as mechanical (pressure wave) energy.

The fluctuating pressures are applied mechanically to all surfaces, causing transfer of mechanical energy to the objects with these surfaces.

The mechanical surface energy is then converted within the body of the object to heat energy by internal processes, as the energy spreads theought the body. In the process the body is warmed the body ever so slightly.
The slightly warmed body will then transfer a small proportion of this heat back to the atmosphere.
This amount is a very small percentage of a very small number.

Note that 'soft' objects absorb more sound than hard ones.

so what happens to the heat that isn't transferred back into the atmosphere? Does that cease to exist? or stay in the warmed body? Sorry to be a questioning pain... i'm trying to get my head around this haha! I'm probably missing a key piece of the puzzle but If the energy that doesn't go in the atmosphere just disappears then surely energy can indeed be destroyed. I think i'm getting there lol

[iNow]

(oversimplified...) Heat is a transfer of energy. What you're describing is temperature. Temperature is basically particles buzzing around and bouncing off one another. The more they buzz and bounce, the warmer the object is. As they buzz and bounce, the collisions are imperfect and some energy drops off... they buzz and bounce slower and slower and slower until eventually they're inline with the ambient temperature in a state of balance or equilibrium. Nothing disappears, it just balances out. This is basically entropy. 

It's imperfect, but I like the analogy of dropping a stone into a pond. It creates ripples that radiate outward and interact with their surroundings. As they go farther and farther, they get weaker and weaker... The peaks and troughs of the wave get smaller and smaller. Sound is not entirely different. It's just a wave through a different medium.

[swansont]

1 hour ago, Half-Dead said:

so what happens to the heat that isn't transferred back into the atmosphere? Does that cease to exist? or stay in the warmed body? Sorry to be a questioning pain... i'm trying to get my head around this haha! I'm probably missing a key piece of the puzzle but If the energy that doesn't go in the atmosphere just disappears then surely energy can indeed be destroyed. I think i'm getting there lol

Heat is energy transfer owing to a temperature difference. The energy remains - it can’t be destroyed - but the heat transfer will cease as the bodies equilibrate.

If there has been net energy transferred into the system the temperature will increase, as iNow describes.