This experiment needs to be done outdoors because no one wants a torrent of water inside the classroom. Academy Curricular Exchange, maintained by the Organization for Community Networks. They have a huge database of lesson plans and activites. Many of the following buttons are linked to lesson plans found on this site. The ones I have listed below are the ones I feel are most engaging and the ones that most closely fit into the Physics catagory.
Students learn to find constellations in the sky and learn their names.
It's difficult to grasp the extreme distances between planets. Most solar system maps are not drawn to scale. Here, students calculate travel time between planets. This is an extremely interesting lesson that uses a balloon and confetti to simulate the Big Bang. The purpose of this activity is to assist students to visualize and better understand the concept of the constant motion of molecules.