Why Do Ships Float? Explore the World of Buoyancy with a Simple Water-Pressure Experiment Device
Science Trainer Ken Kuwako here. Every day is an experiment.
Have you ever experienced that ringing in your ears or that feeling of being squeezed when you dive deep into a pool? That’s the force of water pushing against an object—what we call “water pressure.” But since this force is invisible, it’s surprisingly hard to grasp just by looking at diagrams and arrows in a textbook. Today, I’m going to introduce a super cost-effective piece of equipment that will “visualize” this unseen pressure and even uncover the secret behind “buoyancy.”
Cheap and Highly Effective! The Secret Tool to Visualize Water Pressure
The secret weapon I’m sharing with you today is a hidden gem from the science classroom: the “Simple Water Pressure Demonstrator.”
It’s featured on science material sites like Narika, but its design is extremely straightforward: a clear plastic cylinder with a soft rubber membrane stretched over each side. You might wonder, “That’s it?” Yet, its very simplicity allows us to see the laws of nature with perfect clarity.
Using it is a breeze. Just fill a container with water and slowly lower the device in.
As you submerge it, the water pressure on both sides pushes the rubber membranes inward, causing a noticeable dent. This instantly makes it clear to everyone that “objects underwater are subjected to pressure acting horizontally.”
The Fun Part: Rotate It to Uncover the Secret of Buoyancy
Next, this is where this simple device truly excels: let’s rotate the cylinder 90 degrees while it’s submerged.
This allows us to observe pressure acting not just horizontally, but vertically as well.
As you can see, pressure is acting both up and down. This confirms that objects underwater are subjected to water pressure from all sides. Now, compare the indentation of the top and bottom membranes very carefully. You should notice that the bottom rubber membrane is dented more significantly than the top one.
This happens because water pressure increases proportionally with “depth.” The bottom face, being deeper in the water, is being pushed by a much stronger force. This very phenomenon leads us to a key law of physics. What is the result when you combine the weaker downward push from the top with the stronger upward push from the bottom? Exactly! You are left with a net “upward force.”
This, my friends, is the true nature of buoyancy! “Buoyancy equals the net force of water pressure.” Explaining it this way makes the concept instantly intuitive, even for middle schoolers. The big mystery of “Why do massive ships float?” can be solved by this one simple device.
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My goal is to bring the fun and wonder of science closer to everyone! I’ve put together easy-to-follow guides on fun science experiments you can do at home, along with useful tips. Feel free to explore!
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