Designing an experiment is a great STEM activity for kids. Today we’re trying out a few boat experiments. We’ll talk about boat designs and buoyancy as well as testing how much weight our boats can hold. We’ll also look at propelling our boats using surface tension.
Boat Experiments for Kids
Design a Boat
The first thing you’ll need to do is design a boat to use in your experiment. Head over to my post on How to Build a Boat for design suggestions and material ideas.
You could start with a simple piece of craft foam or even some aluminum foil if you wish. Or try your hand at a more complex design.
Experiment #1: Will the Boat Float?
After designing and building your boats, you’ll need to see if they can float. Fill a bowl full of water or head to the bathtub and test out your boat designs.
If your boat sinks, why? Are the materials too dense? Is the boat taking in water or is there a leak? Are the materials soaking up the water?
Make changes to your designs if needed.
Experiment #2: How Much Weight Will the Boat Hold?
An experiment involves testing ideas and manipulating variables. In this experiment, we are testing which boat will hold the most weight. We are changing only the size of the boat.
We made our boats out of foam sheets from the craft section of the store. You can use the boats you designed for experiment #1 above, you can use foam sheets like we did, or you can use aluminum foil. Check out the Buoyancy Boats in the Fun STEM Activities on a Budget post for an example of aluminum foil boats.
Make your boat design in 3 or 4 different sizes. We simply cut a flat boat shape out the foam sheets.
Place the boats in some water. (Double check that they float.)
Add weight to each of the boats. We used washers for our weights. You could also use pennies.
All of our boats fit together in kiddie pool, so we tested them at the same time. You may need to test your boats one at a time.
How much weight can each of your boats hold? Record the amount on a piece of paper.
My kids predicted that the larger sized boats would be able to hold more weight. They were correct. However, my kids think their boats should have held more water than they did.
Since our foam sheets were flat with no sides, water easily got on top when the boat was pushed down by the weight.
Below you’ll see two of their boats underwater.
Here’s a new experiment to try: does a boat with taller sides hold more weight than a boat with shorter (or no) sides?
This would be a great time to talk about buoyancy and displacement. Try this boat experiment that compares clay boats with different shapes and volumes.
Experiment #3: Soap-Powered Boats
For this experiment, you’ll need a foam sheet (or a flat piece of Styrofoam, juice carton, or plastic from the recycling bin). You’ll also need scissors, dish soap, and a container of water.
Cut out a boat shape. We used the same design as in experiment #2 above. We also cut a notch out of the back of the boat. Our goal was to test which design worked better.
Place the boat on the water.
Add a drop of dish soap behind the boat. If you cut a notch in the back of your boat, add the drop of soap into the notch.
The boat should race across the water. We found that the boats with a notch traveled faster than the boats with a straight back.
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This is due to the change in surface tension. The soap contains surfactants which lowers the surface tension of the water. The surface tension is higher at the front of the boat, so the boat is pulled forward.
Once the soap spreads through the water, you won’t be able to try it again. You’ll need to empty the container of water and refill it. Then, you can race your boat again.
Instead of dropping the dish soap behind the boat, you could use a toothpick to spread the soap on the back of the boat. Then, place the boat in the water and watch it race around. Check out this video of a leaf boat being propelled by soap.
Experiment with different shapes of boats or different materials. You could also try to use something different in place of the soap to reduce the surface tension. What about trying vegetable oil or salt?
More STEM Activities for Kids
Finally check out the best activities for our Math and Science Night. I wanted to include a variety of math and science concepts, accessible to lower grades (K-2) and then others to appeal to the upper grades (3-5).
For math, we prepared the the following 10 math activities (all available in the packet here). The activities and games are included with instruction sheets, materials list, and printable sheets and scoresheets:
1. Chutes and Ladders Game (addition/subtraction 0-20)
2. Shape Architect (shapes, vertex, edge, face)
3. Perimeters in Pieces (perimeters, measurement)
4. Horse Races (with dice; addition or multiplication)
5. Tangrams (shapes, spatial reasoning)
6. Math Races (mental math, addition/subtraction)
7. Fractions in Baking (adding and subtracting fractions)
8. Logic Game (strategy)
9. 100s Dice Game (choose to play with addition, subtraction, multiplication or division depending on level)
10. Decimal Riddles (decimals, fractions)
The following 12 science activities and games are included in the packet here, with instruction sheets, materials list, and printable sheets:
1. Kitchen Chemistry (predictions, acid/base chemical reactions)
2. Balloon Blow-Up (observations, acid/base chemical reaction)
3. Fly a Helicopter! (forces of flight, trial and error)
4. Make Ice Cream! (states of matter)
5. Buoyancy Boats (floating, sinking, buoyancy)
6. A-MAZE-ing Q-tips (angles, engineering)
7. Squishy Circuits (electrical energy, circuits)
8. Tower Challenges (engineering, physics)
9. Save Fred! (flowcharts/sequencing of operations, problem solving, teamwork)
10. Mining Cookies (problem solving, using tools, charting results)
11. Penny Problems (structural engineering, teamwork)
12. Seeking Seeds! (plant biology, adaptations, bar graphs, percentages)