Physics Help Forum Explain sound to a kid.

 Waves and Sound Waves and Sound Physics Help Forum

 Aug 24th 2017, 08:27 AM #1 Senior Member   Join Date: Feb 2017 Posts: 161 Explain sound to a kid. What is sound? Sound is vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear. We can show this kid a car that plays loud music. This car vibrates so you can say it is shaking because sound is vibration. Is my observation correct?
Aug 24th 2017, 08:39 AM   #2
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 Originally Posted by avito009 What is sound? Sound is vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear.
While true its insufficient to describe what sound is.

Sound waves are alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction of air

https://en.wikipedia.org/wiki/Sound

 Originally Posted by avito009 We can show this kid a car that plays loud music. This car vibrates so you can say it is shaking because sound is vibration. Is my observation correct?
Not exactly. It's not the entire car itself which is vibrating. Its the speaker inside the car which is vibrating generates the sound waves. I.e. the diaphragm of the speaker compresses and rarefies the air that its in contact with. Some of the vibrations caused in this way are transmitted to the body of the car itself which in turn causes sound but is barely audible.

Aug 24th 2017, 09:52 AM   #3
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 Sound is vibrations that travel through
I prefer the phrase "spread out through".

Travel through suggests a definite localised something like a train or a car that is only in one place at a time and moves on from one place to another.

Sound is different because it may start off at a source but eventually occupies the entire medium, if left alone.

As simple experiment for the child is to observe that the same sound can be heard from lots of different places at once.

Another is to measure the speed of sound by observing the time lag between seeing the lightning and hearing the thunder of a distant storm.

Another feature of sound is that there are many different types of sound, determined by their pitch or frequency.

Another good game is to show that sound can be deflected eg round a corner (you can hear round a corner but you can't see round one) and reflected eg echoes.

Last edited by studiot; Aug 24th 2017 at 09:55 AM.

 Aug 24th 2017, 10:52 AM #4 Senior Member     Join Date: Jun 2016 Location: England Posts: 366 A good way to demonstrate the link between vibrations and sound is the old fashioned big speaker with rock music. Give the kid ear defenders (health and safety first) then put them in front of a powerful sound system and play some loud music. Let them feel the sound in their stomach. Alternatively (and better for the neighbours) get a scrap-able speaker (one that you don't care if it gets fingers poked through it) and have the kid feel the speaker as it plays (modestly loud) music. A third option has just occurred to me. In the film on the life of Helen Keller (deaf & blind girl) they had a scene showing her learning about sound and speech, by humming with their lips against a balloon she was able to feel the balloon vibrate in response to the humming. __________________ ~\o/~ Last edited by Woody; Aug 24th 2017 at 10:54 AM. Reason: spelling
 Aug 24th 2017, 11:08 AM #5 Physics Team   Join Date: Apr 2009 Location: Boston's North Shore Posts: 1,278 By the way. If a tree falls down in the forest and there's nobody around to hear it then it does make a sound.

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