Hands-on Science Carnival Activity Stations: Pressure and Buoyancy

Aluminum Foil Boats

[Shopping List: aluminum foil; scissors; large, flat basin for water; 5 gallon bucket; dry pinto beans or another weight; random sample of items that sink/float to demonstrate]

1. Show the kids items that sink and float in water, discussing possible reasons behind this. Wad up a piece of aluminum foil and show that it will sink in water. Be sure to squeeze it tightly or fold it up to make sure there isn't a lot of trapped air that will make it float.
2. Provide each kid with a piece of aluminum foil ~12" square, and ask them to fold it into a boat of any shape.
3. Test finished boats in the basin of water, placing dry pinto beans into them to determine carrying capacity.
4. Encourage kids to refold the foil if the boat doesn't work

What's Happening: Buoyancy is the ability to float in a fluid – kids might be familiar with the "does it sink or does it float" activity. Buoyancy is dependent on density and surface area. Gravity pulls the boat down, displacing some of the water in the basin. Boats float because the mass of the water they are able to dispace is greater than the mass of the boat and cargo – carrying capacity is determined by how much water is displaced by the hull. A boat with a large volume will displace more water than one with a small volume, enabling it to carry more cargo. Similarly, it is easier to float in salt water than fresh water because salt water is denser (more mass per volume because of the salt), therefore less water needs to be displaced to balance out the force of gravity.