4 plastic cups
sturdy stick (could use a chopstick)
1. Insert stick inside of straw
2. Tape straw to center of the ruler (back)
3. Tape ends of stick to bottom of 2 of your cups
4. (for balancing scale): tape the bottom of the other 2 cups to the the top of the ruler
You can compare objects' weight or catapult something! Check the experiment out over at Jameson's Lab!