This is the 2911th most frequent Japanese word.
わく
"わく" means "frame" or "border" in English.
Here, 'わく' is used in the sense of feelings or emotions arising spontaneously.
気持ちがわく。
Feelings arise.
In this sentence, 'わく' means to boil or to heat something until it reaches boiling temperature.
お湯がわく。
The water boils.
This usage of 'わく' describes the emergence of interest or curiosity naturally.