Inside: All you need to make a raft are a few natural items you can find in your own backyard or local park. You’d never guess this is a great introduction to physics and can keep your kids occupied for hours.
We love floating our fun DIY, eco-friendly, and completely biodegradable stick rafts! And I say “we” because I’m right in there with my kids floating my raft and feeling like a kid again.
I’m not sure what it is exactly, but I find the whole experience extremely relaxing. Placing the raft just right in the water, moving my hands slowly away and holding my breath until it’s clear that the raft won’t capsize.
The hardest part?
To let the raft float into the sunset. And don’t worry; in contrast to store-bought toys, you can let your raft drift away without any harm to the environment. How come? It’s because our rafts are made of sticks, grass, and leaves.
It may seem like an idle way to pass the time, but in reality, it’s super educational.
This stick raft project will help your kids practice:
- Gross motor skills (while collecting sticks, building a raft, and wading in the water floating the raft)
- Investigation and inquiry (exploring multiple ways to create a raft, trying to predict an outcome, and drawing conclusions from unsuccessful launches)
- Attention and persistence, even if there are problems like capsizing due to uneven weight distribution,
- Judgment and decision making (identifying and troubleshooting solutions: is the raft balanced enough to float, can a mast be moved left or right to a better position, etc),
- and finally, perhaps most important of all, joyous exploration and engagement in challenging tasks simply for the sake of challenge and experience.
How to Make a Stick Raft
What you need:
If you like shortcuts, replace grass with cotton yarn. It makes connecting sticks easier and faster.
What to do
1. Gather sticks
Go for a walk and gather sticks that are about the same length and thickness.
Note: You might be as surprised as we were to discover that most sticks are not straight. They look pretty straight, but when you lay them down next to a ruler, you see the difference.
We did a bit of research and found out that the shape of a stick is determined by the interplay between the tree’s desire to reach straight up to the sun and the gravitational pull that (you guessed it) pulls it down to the ground. So the fresh part of the stick at the outer edge bends up, but the rest of the branch is more parallel to the ground.
2. Tie sticks together
Use long grass to tie sticks together on both ends. We live in the Midwest, where long grass abounds. However, if you can’t find grass long enough to tie sticks together where you live, you can use another natural material, plain cotton yarn (it’s biodegradable within 5 months).
Just remember that if you use something like plastic cords or painter’s tape, you can’t leave the raft to float away. It’s dangerous for fish and sea birds.
3. Add Mast
Skewer a leaf on a thin stick, and push “the sail” between the middle two sticks. Depending on how heavy your stick is, you might have to add a crisscross of a few blades of grass around the “mast” to keep it steady.
4. Test in water
Test it in the bathtub, pool, river, lake, or ocean.
After playing with it for hours, let it go!
Stick Raft Troubleshooting
The problem we kept running into at the beginning of our raft building was capsizing.
The most common cause of the capsizing is uneven weight distribution. So, if your boat is capsizing, look at it carefully: are the sticks on one side longer/ wider/heavier than on the other side?
Can you add another stick (or two) to see if it fixes a problem? Here you can talk to your kids about the thickness of sticks, approximate weight, balance, and symmetry.
Keep trying. It’s fun! No engineer ever built the perfect construction on the first try.
How to calculate weight distribution in physics is beyond the scope of this post, but there are quite a few very interesting scientific concepts to talk about with small kids in this activity.
The Science of Stick Boat
Did you know that stick rafts have been around for thousands of years? Historians believe that the first crafts were made 1.8 million years ago when Homo Erectus (the first of our relatives to have human-like body proportions) started to leave Africa and spread east to China and Indonesia.
Boats can be useful for transportation, fishing, and exploring, but what makes boats float?
What makes something float or sink? This is a very cool physics question that we will briefly explore below.
To understand why things float, you need to understand buoyancy. Gravity works in the water in the same way that it works in the air, but objects in the water have some buoyancy force pushing against gravity.
Buoyancy is a force exerted by the liquid that pushes up against the object you place in it. Think of it as resistance: the water doesn’t readily accept the log coming into it from the air. Since air is far less dense than water, it makes sense that it would be easier to move something through the air than into water.
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So, how much resistance are we talking about? Can we calculate it? Archimedes (a brilliant physicist from Ancient Greece) figured it out. The upward thrust of buoyancy is exactly equal to the weight of the water displaced by the object.
Again, this makes sense: you’re asking some water to get out of the way of your object, and it’s only going to do that if the object is heavier, that is, if it has more gravity working on it than the water does. This is called Negative Buoyancy: the object has more gravity pulling it down than the water has resistance to it.
In Positive Buoyancy, buoyancy wins, and the object floats. In Neutral Buoyancy, the object’s weight is the same as the weight of the displaced water, so it can just sort of float underwater.
Lucky for us, water is very heavy, which means it will exert enough of an upward thrust to let us float all kinds of things on it – from stick rafts to gigantic iron ships! And us! Humans are mostly water, but we also have air inside us. If you take a really deep breath when you’re swimming, you’ll find you can just float on the water!
Ever been SCUBA Diving? You’ll need to wear some weights around your waist, so you’re heavy enough to stay underwater and achieve Neutral Buoyancy!