If you have never spent time looking at the history of Archimedes you’re missing out on a really cool piece of research. One thing Archimedes is often remembered most for is his exclamation, “Eureka, I’ve found it!” just after he realized how to best determine whether a king’s crown was pure gold or a mixture of gold and silver. Unfortunately, there was a certain jeweler/crown-maker that lost his head after the discovery. Anyway, be sure to read the story for yourself on any number of websites.
One way to show the principle of buoyancy is to build Archimedes’ boat. This is actually a pretty simple exercise for students in high school, but may present some challenge to children under eight. Remember, challenges are often good for students and give them a sense of accomplishment once they have overcome them.
The materials needed for this lesson include a 12” x 12” square of aluminum foil (the thicker foil will work better than the thinner type), a pan, sink, or bathtub to hold water, and several small objects (pennies, quarters, and nickels work well as do washers).
1. Have the students build a boat from the sheet of aluminum foil. Don’t help them with the process; it’s important to allow inquiry learning among students.
2. Fill the pan, sink, or bathtub with enough water to allow the boat to sink.
3. The students should now check the boat’s ability to float. Once they are certain it will float, have them start the process of adding the small objects to the boat. Coins or washers are best for this since they offer weight in a small volume.
4. Students should continue adding weights, keeping count of the amount of money in the boat (if using coins) or the number of washers. Make it a competition between the students!
5. Once the boat begins to take on water, stop adding objects. The students will need to calculate the amount of money or number of washers that were in the boat right before it began to take on water. They should not count any coins or washers added while the boat was sinking.
6. For all students, a discussion on what causes boats to float would be a great idea. Remember to discuss buoyancy, which is the force acting in opposition to gravity in the water. Ask the students how buoyancy could be overcome. Many of the students middle-school aged and up will be able to make the connection between the boat floating and the boat sinking. They can find the buoyant force on the boat by calculating the total weight in the boat before it sank. The weight that causes the boat to sink was great enough to oppose the buoyant force.
7. Finally, ask the students if the shape of the boat would affect the buoyant force. Give them another sheet of aluminum foil and encourage them to try another design.
The students will have a great time with this, but so would adults. It’s a great way to do ice-breakers at backyard parties where a kids’ pool would be available. Give it a try! It’s a wonderful way to involve both the kids and the adults!