There are several reasons for doing lecture demonstration videos. Firstly it is to engage the student in a practical, hands-on demonstration performed by either the teacher or with encouragement and guidance from the teacher, by the student. Kinaesthetic learning. Secondly it is a way of allowing the teacher to use the discipline specific words related to this phenomenon in context. Jargon. Thirdly the demonstrations can be used to provide the students with an opportunity to observe and experience so they can make informed comments and ask informed questions about the underlying science. Fourthly they can be used as counter-demonstrations to highlight for the student any misconceptions they may have about the underlying science. In all of these scenarios conversation and discussion are the key to learning.
Students need to learn the precision with which the words of the discipline are used to be able to communicate effectively. This takes time and practice. The words velocity, acceleration and momentum are not interchangeable so hearing how they are used in context and then practising their use during discussion, and in writing, helps students understand the deeper meaning associated with those words.