Teams of 2 or 3 Scouts are presented with the basic equipment and have to make a steam mortar.
A log floating in a bucket of water, a hand axe, a small tin with tight fitting lid (eg syrup tin ), a limited number of matches in a box.
Use the axe to split the log into smaller and smaller pieces of wood, build and light a fire. place a small amount of water in the tin and put the lid on reasonably tight. In a few minutes the lid will be blown off the tin a metre or so into the air. ( As confidence in the process builds then the lid can be secured a bit tighter for a higher projectile of the lid ! )