Science of The Arts 2017 | Sound Waves 💥

Aim: I want to find out about what sound waves are.

Research: A sound wave can be defined as a wave, invisible to the human eye, that can travel through all different forms of mediums; a medium can be air, a body of water, walls, doors, glass, wood, etc. Certain mediums are better to be heard through than others. The only place sound cannot be heard is in outer space, due to the lack of air in the atmosphere. 

How are sound waves generated?
Sound waves are generated by a vibration, which disturb the molecules around the source. An example of this is human vocal cords. When air passes through your vocal cords, a process called phonation, they vibrate and produce the sound waves that are heard by other humans as your voice. Sound waves are unable travel forever. This is because they eventually lose energy, weaken and distort.

What is pitch? 💭
All pitches of sound are generated by the length (short or long) of these sound waves. This term is called "wavelengths". The longer the wavelength, the deeper and lower pitch. The shorter the wavelength, the higher the pitch. 
The way pitch is measured is by the amount of wavelengths travelling through the air every second. This is called 'frequency.' Humans can hear frequencies (numbers of wavelengths) from 20 Hz up to 20,000 Hz. 
Frequencies below 20 Hz are called 'infrasonic', while frequencies above 20,000 Hz are  called 'ultra sonic'. 

Experiment 💥: 
The famous scientist named Robert Boyle conducted an experiment to demonstrate sound waves back in the 17th century. Boyle placed a ringing alarm clock inside a large glass car with a 'valve' on top. He used a vacuum pump to remove the air, and by doing this he demonstrated how sound needs air to be carried. 

Equipment to conduct the experiment:
- Alarm clock or cellphone
- Large glass jar with valve
- Vacuum pump

Equipment for the vacuum pump:
- Mason jar (with 5mm hole in centre of lid)
- Syringe
- One way valve (bike valves)
- 5mm flexible tubing 


Method: 💣💥
1. Place the ringing phone or alarm clock inside of the jar with the lid on as tight as possible, ensuring no air can escape or get inside.

2. Using the vacuum pump through the hole in the lid, 
suck of all the air out of the jar. Make sure there is no gap between the hole and pump to ensure no air can get in. The alarm clock's ringing will fade out as more air is sucked out and sound waves are distorted.
3. As the air is released back into the jar, the ringing will be able to be heard again as the air becomes a medium to allow sound waves to travel.

Below is what the experiment looks like in action - with proper equipment!






Explanation
My experiment was successful after a number of attempts, and definitely displayed how sound waves work. 

I first attempted to create a bell vacuum jar at home. The equipment I used for this was a mason jar with a hole in the lid and 10ml syringes. The bell jar didn't work. The reason for this is that the syringes were not big enough to suck all of the air out of the jar. For example if the syringes had a volume of 60ml, the volume would be large enough to suck all of the air out of the car. The 10ml syringe's volume was too small to be able to successful suck all of the air out of the jar.  
After realising my mistake and looking for a syringe with a larger volume, I eventually found a balloon pump. The pump had an approximate 100ml volume and would be able to suck all of the air out of my jar.
However, this also failed. My first mistake is that the seal I made around the jar's hole and pump was not air tight. I had to use a resource like blue tack or slime to make sure it was air tight and no air could escape. My second mistake was that the balloon pump was the incorrect way. The way I was holding it resulted in air being pushed into the jar, not out. I recognised my mistakes and was able to conduct a successful experiment.
The seal I used was Blue Tack, which was air tight. I held the pump differently to suck the air out, and got to use a real bell jar for the experiment.
On my first attempt of the experiment, there was a small mistake as I didn't put the phone on an object. Sound waves travel through materials and so it could still be heard because the sound was travelling through the table. 

The pump was able to suck most of the air out of the jar. The phone inside making a noise lowered in noise considerably, so even though the pump's volume was not big enough to suck all of the air out of the jar, it got most of it out. The lack of air in the jar resulted in the jar being stuck to the table, because there was a vacuum.

Why did this happen?
Sound waves travel though a range of different things, including air. The seals on both the bottom and valve of the jar were air tight, and so when the pump began to suck out the air, the sound did not have anything to travel through. No air in the jar meant vibrations, which sound is made from, could not occur. 
As the air was released back into the jar, the sound waves had something to travel through and could be heard again. The phone could not be heard ringing because of the lack of the medium, in this case it was air, to carry the sound waves inside of the jar.