system
Given the following post, respond as if you're commenting on Reddit:
human
If sound is the vibration of the air, and the state of matter is determided by how much it's molecules vibrate, can sound melt something?

Even if you'd need a impossibly high pitch, is it theoretically possible? I feel like I'm forgetting something very important about how heat works.
gpt
Yes, ultrasonic welding is a method of solid state welding where the material such as plastic between two parts are melted together. The sound vibrates at a high frequency, at the low kHz, to heat up the plastic where it is pressed together in a vice or a press. No glue or soldering needed to meld them.