When would the velocity of a wave traveling in a medium change?

Well, hello there, friend! Waves are like happy little dancers moving through a medium. The velocity of a wave can change when it enters a new medium with a different density or elasticity. Just like how a gentle breeze might slow down when it meets a field of flowers, waves adjust their speed as they encounter new surroundings. It's all just a beautiful dance of nature, full of surprises and wonder.