MIT Tech TV is a collection of thousands videos produced by students and faculty at MIT. The videos are arranged into more than 600 collections covering topics in engineering, education, science, the humanities, and more. You can view the videos online and most of them are available to download.
Roughly 300 of the MIT Tech TV videos are also available on a YouTube channel of the same name. There are a couple of playlists within the channel that could be of interest to high school and middle school science teachers. MIT Engineering K-12 is a set of twenty-six videos in which MIT students explain and demonstrate things like gas pressure, gravity, Boyle's Law, and the shape of sound waves.
MIT Physics Demonstrations is a playlist of 44 short demonstrations. The videos don't have narration, just the demonstration. The explanation of the principle demonstrated is found in the description below each video.
Applications for Education
The MIT Physics Demonstrations videos could be helpful if you don't have access to the materials necessary to do the demonstration in your classroom. The videos could prompt your students' questions or you could ask students to research the answers to questions based on the demonstrations.