Take the Aluminum boat buoyancy challenge. Start with a 4″ by 4″ piece of aluminum foil. Then use that piece to make a boat that will hold the most pennies as possible without sinking. See which designs hold the most. My niece Amber was able to hold 20 pennies. This challenge will make you explore how the size affects how much weight they carry and how this relates to the density of water. Try this with salt water to see if you can hold more pennies?