A fantastic resource for Educational videos, lessons and games for K-12 students is neok12. This site organized by curricular topic is packed with resources and information.
A quick test of the topic Forces brought me to a shortened version of the Wikipedia articles on Types of Forces, Images from Flickr tagged under Creative Common Licensing, Quiz Games, Online Games and Puzzles and Videos. While I would be careful of the images as they are taken from Flickr and not an entirely trusted site, the videos are all reviewed by K-12 teachers and ones that seems to be short in length, appealing and educationally correct. The collection ends with related topics at the bottom of the page that I could really see students getting very excited about. The website itself offers a ChildSafe Watchdog Guarantee and indicates that all lessons and videos have been screened for K-12 use. RY