The vibration is changed by either reducing the length of the string (holding it down on a fret) or changing the tension of the string.
The volume is changed.
It will be reduced.
In a small volume container the pressure is higher.
The concert sized ukulele was developed in the 1920's to provide a bit more volume for vaudeville audiences.
A banjolele is a stringed instrument that combines the ukulele with the banjo. It provides more volume than a standard ukulele and was very popular in vaudeville.
Yes if the both are not changed proportionately, Density = mass/volume.
This is a physical change.
That depends on the type of instrument you are talking about. An electric ukulele used pickups and no sound hole is required. However, an acoustic ukulele is going to need to have holes to provide volume by allowing the sound to project out of the instrument.
in gases, change in volume is a physical change. however you can manipulate it physically or chemically (to a loose definition). Look at the ideal gas equation. PV=nRT Volume is dependent on pressure and temperature (physically changed) and on the number of moles (amount of gas) (chemical....ish)
If only the length is changed and all other dimensions left unchanged, the volume will also triple.
The shape of a liquid can be changed by putting it in a different shaped container. The volume can be changed (although hard to do) through extreme pressures and tempatures.
It can be played either way. Typically when accompanying other musicians, single notes are played. The 'bass' ukulele is usually amplified to get enough volume.