Defend your kingdom! Students try to build a catapult that can launch a cotton ball "boulder" at the enemy that is located exactly one foot away. Easy to find materials include Legos (or other materials, such as cardboard, tape, etc.), a ruler, and a cotton ball to build the catapults. Students test out their catapults and measure the distance the cotton ball lands from their catapult. When they think they have an accurate catapult, they can try it out against a Lego troll (or other figure t