I selected this for second grade but in fact this website (thekidsshouldseethis.com) is awesome for any kids. They hold a huge library of learning videos for any subject area. One of the many videos that caught my attention here is the “Zero Gravity 360 degree+ Weightless Water Experiments” in which they show experiments in a refitted reduced gravity aircraft. They discuss weightlessness, training astronauts before spaceflight and more.
This is just one of the many cool videos to find here!