Over the years, we have done so many STEM and STEAM activities and challenges in our house. Some went along with our science lessons, but most were just for fun. The make it float Cargo Boat STEAM challenge is a lot of fun, plus it teaches kids about buoyancy, displacement, force, and Archimedes principle. It also solves the mystery of how a boat can carry a cargo that weighs far more than the boat itself.
Let’s jump in.
This post contains affiliate links.
Why Do Boats Float?
To learn why boats float, let’s do a simple activity. You will need 2 glasses of water, a couple ice cubes, and a penny.
First, mark the water levels in both glasses. Then, place the ice cubes into one glass of water. Drop the penny into the other glass of water.
The ice cubes should float and the penny should sink. Why?
Did you notice the water level rise in the glass when the ice cubes were added? (The level rose on the glass with the penny as well, but just not enough to notice.) This is because when an object is place in water it pushes some of that water away. This moving away of the water is called displacement.
When an object is placed into water, two forces act upon it – gravity and buoyancy force. Gravity is pulling the object’s weight to the earth. Buoyancy force is pushing the object upward. Archimedes principle states that buoyant force on an object in a liquid is equal to the weight of the liquid that is displaced by that object. When an object weighs less than the amount of water it displaces, it floats. This ability to float is called buoyancy.
So, the ice floated because the weight of the water it displaced was more that the weight of the ice. The weight of the penny was more than the weight of the amount of water it displaced.
Boats float when they weigh less than the water they displace.
Cargo Boat STEAM Challenge
Boats are designed according to their use. Cargo ships often carry more than their own weight, so they need to be designed so they can do just that. Their flat, shallow design keeps them buoyant even with large loads.
My challenge to you is to create a cargo boat out of aluminum foil that will carry a weight much greater than itself.
Here is how we did ours. You can be as creative as you want. In fact, please add your own flair!
Container of water
Create a boat from a piece of aluminum foil. We used the design of the river barges that haul goods on the nearby Illinois river. It is what was familiar to us. By all means, try your own design! If you have a scale, weight it. Our boat was 0.89 grams. I should have measured the dimensions of the piece of foil before we started. Feel free to do that.
If you Google the weight of a penny, it says the average penny is 2.5g. You can use that weight or if you want to add another dimension to your project you can take 10 of your pennies, weigh them and then get the average weight to use in your calculations. The average weight of my 10 pennies was 2.62 grams.
Next, place your boat in the container of water. We used a baking dish. Add pennies until your boat sinks.
Count how many pennies it took to float the boat. It took 32 pennies to float our boat. If I use our average of 2.62 grams per penny, the total weight of the pennies added was 83.84 grams. Add the weight of the boat, 0.89 grams, and we can calculate the weight of the water displaced just before sinking was approximately 84.73 grams. We can also see that the boat held approximately 94% of its weight before sinking!
Where your results similar?
Did it matter where you placed the pennies in your boat?
Did you boat tip over before it sank? If so, what design changes could you make to stop this from happening?
Could you design the boat differently to hold more pennies?
Make It Your Own STEAM Challenge
Try this challenge on your own. Get creative with the boat. Make it larger. Give it a sail, a flag, or other features. Make it out of something different than aluminum foil. And…let me see it!!
STEAM At Home Challenge
Go check out their awesome STEAM Challenges, too!
Geek Pack Hack – Make It Go STEAM Challenge
Gift of Curiosity – Tower Building Challenge
Igamemom – Egg Drop Challenge
Check out these awesome engineering challenges, too!