I do not think that a sound has to be heard in order for it to be considered a sound. Sound is not only heard, but felt. Sound consists of vibrations and most certainly as the tree fell there were tremendous vibrations occurring because of the sound it made.
This question can certainly be examined in a philosophical sense. In other words, if the sound is not heard then it may be plausible to say that it did not make a sound. In reality, this really does not make a lot of sense to me because like I said before, sound does not need to be heard to happen.
"Sound is a traveling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard."
You can analyze this question in two ways. You can look at it scientifically or philosophically. Above is a definition of what sound is.
Scientifically speaking, sound is an actual occurrence. If this is true, then if someone is present or not to hear it, it occurred.
Philosophically speaking, if no one was present to perceive the event one might contend that it did not occur. I am a believer in science. Although a human may not have been present to hear the event, animals were. In addition, matter was present for the sound wave to travel through.
In my opinion, it does. Physically speaking, it surely must. It is only philosophically that you can argue that it does not, in my opinion.
A sound is simply a physical wave. When the right conditions occur, a sound wave is created. The sound wave exists regardless of whether someone is there to perceive it. So physically speaking, I do not see any way that a tree falling would NOT make a noise.
However, if you say that a sound is different from a noise, then perhaps the tree does not make one. If you say that a sound is our perception of a sound wave, then the tree would not make a sound.
This question is rather philosophical. It can be put into a general question, "Is a physical phenomenon producing sound a sound, even if there is no one to hear it?" The question can be then extended to other senses. For example, we can ask "Is a spoonful of sugar sweet if no one ever tastes that specific sugar in the spoon.
I would personally believe that the physical event or attribute exists independent of whether or not there is someone to witness and perceive that event or attributes. To understand why this is so, let us assume that the sound of the failing tree has not been heard by any one, but has been recorded in a tape recorder. Now, can we say that the original sound existed only if someone later hears the recorded sound of falling tree. It is clear that the sound was created and recorded when the tree fell and not when someone heard the recording.
Yes it does make a sound... if everyone were to evacuate a city because of a hurricane and a tree fell of course it would still make a sound even though no one is there to hear it. its not like invisible... its a tree even if a pen falls it still makes a sound... stupid question