Identifying your type of instrument

My instrument that I created for this Junk Band project was called the pop-tar. It included a two liter bottle, string, and a dowel (or any type of wood that was stable) preferably a pencil. The stretched string from the bottom to the top of the bottle vibrates as you pluck it. This causes the bottle(soundbox) to vibrate, which leads to the air vibrating so you can hear the sound. Stretch the string tighter by turning the dowel at the top and the pitch becomes higher. Turn it in the opposite direction to make the pitch lower. The tighter you turn the dowel the more compressed the plastic gets which leaves little space for the air to vibrate off of which makes the sharper sound. Plucking hard on the string means putting a lot of force and energy into the pluck making the string vibrate a longer amount of time. My defects in this project was the amount if time i had to spend the dowel in the performance. And the higher pitched instrument  over powered mine.