I know that mechanical waves need a medium to travel through, but what happens when there is no medium and how does it it follow the first law of thermodynamics ?
In: Physics
It stays in whatever object is making the sound, whatever that is. If you bang some metal in a vacuum, the waves just stay in the metal. When a wave reaches the edge of the metal, it completely turns around. This continues util that the waves are completely scrambled and incoherent, which is just another way of saying it turns into heat.
Notice how you can see your reflection in glass? That’s because light travels slower in glass than air. The bigger the difference in the speed of a wave between two things, the more the wave reflects. Same applies to sound. Some sound bounces off a wall when some goes through, and it depends on how fast the sound travels in the wall. Steel would reflect more than wood, as speed of sound in steel is about 5000 m/s and wood is 4000 m/s. Air for comparison is about 330 m/s.Since sound can’t travel in a vacuum, it all reflects.
You can visualize this as you flipping a rope up and down, and making a wave travel along it. Or better yet, go grab a rope and attach some things to the end. Attach the end of the rope to a concrete block, and when your wave hits the concrete block, it’s not going to budge, so the rope will reflect the wave back to you. The rope in your hand will start to move a lot well after you gave it a shake. Attach a heavier chain to the end, and some of the wave will go into moving the chain, some will reflect to you. Just attach more of the same rope, and the wave won’t reflect back at all, it will just continue down the rope until it dies off. You’ll feel no further shaking of the rope. Attach a light string, and some will go into moving the string, but some will bounce back to you. Attach nothing to the end of the rope, and the wave will sort of whip at the end, bounce the wave and come back, and wiggle the rope in your hands some more. That’s sound hitting a vacuum.
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