What does tightening a string on violin do to the sound made by that string?

When a string on a violin is tightened, it increases the tension of the string. Higher tension results in a higher frequency of vibration, which in turn produces a higher pitch. The tighter the string, the higher the pitch of the sound it makes. Conversely, loosening a string decreases the tension and lowers the pitch. Adjusting the tension of the strings is a crucial aspect of tuning a violin and ensuring that it produces the correct pitch.