How Submarines Sink and Float
How Submarines Sink and Float — an illustrated science story, set in United States. 10 illustrated pages, free to read on Wonder Science.
Page 1
Zahra watched a massive container ship glide across the San Francisco Bay. The phenomenon of buoyancy is at play, keeping this giant afloat. But how? It seems impossible that something so heavy can float on water. In fact, some container ships are longer than the Empire State Building is tall!\n\n Fact: A container ship's buoyancy depends on its hull shape and the volume of water it displaces. This principle allows ships longer than the Empire State Building to float despite weighing hundreds of thousands of tons!
Page 2
Back home in Noe Valley, Zahra was taking a bath with her toy submarine when it sank to the bottom. She wondered why the massive ships floated but her small toy didn't. She asked her dad, who was reading a book on the couch, "Dad, why do big ships float, but my submarine sinks?" she asked, perplexed.\n\n""That's a great question, Zahra!" her dad replied. "It all comes down to something called buoyancy. We'll have to investigate.""\n\n Fact: Fun Fact: Light takes 8 minutes and 20 seconds to travel from the Sun to Earth. Maybe that's why it seems like it takes forever for bathwater to cool down!
Page 3
Zahra's dad pulled out a notebook and said, "Let's look at what Archimedes figured out a long time ago." He opened the book to a page about Archimedes and said, "'Eureka!' as Archimedes famously shouted when he discovered the principle of buoyancy. It changed how we understand floating objects, like ships, forever."\n\n""Archimedes was a Greek mathematician, physicist, engineer, inventor, and astronomer," Zahra's dad explained. "He lived over 2000 years ago. His principle explains how objects float or sink.""\n\n Fact: Archimedes' principle, formulated in ancient Greece, is still fundamental to naval architecture today.
Page 4
Zahra's dad began to explain, "Imagine a submarine sitting on a scale, but underwater. Now imagine an equal volume of water also on that scale, but not underwater. The weight of that volume of water is the buoyant force pushing up on the submarine!" He showed her a diagram in his notebook.\n\n""The key is displacement," he said. "An object floats if the buoyant force—the weight of the water it displaces—is greater than its own weight. And that means that the overall density is less than water!" Zahra started to understand."\n\n Fact: Density is mass per unit volume. If an object is less dense than water, it floats; otherwise, it sinks. Ships are designed to maximize their volume relative to their mass.
Page 5
Her dad showed Zahra how a submarine could change its buoyancy. "Submarines have ballast tanks," he explained. "By filling them with air, the submarine displaces less water, making it lighter and able to rise. By filling them with water, it displaces more, sinking the submarine."\n\n"He drew a diagram of a submarine with ballast tanks filling with water and air. "See how the arrows representing the buoyant force change?" he asked."\n\n Fact: Submarines control their depth by adjusting the amount of water and air in their ballast tanks, effectively changing their overall density.
Page 6
To demonstrate, Zahra's dad took her to Everett Middle School where Mr. Harris, the science teacher, showed them a model submarine. He pumped air into the ballast tanks, and the model rose to the surface of a tank. Then, he let water in, and the submarine sank. \n\n" "This is how submarines explore the ocean depths," Mr. Harris explained. "They change their density to dive and surface!""\n\n Fact: Ballast tanks were essential for the invention of the first true submarine by Cornelius Drebbel in the 17th century, though his design was quite different from modern submarines.
Page 7
Zahra imagined a real submarine, a deep-sea research vessel, exploring the Mariana Trench, the deepest part of the ocean. She saw the submarine silently navigating through the dark waters, its lights illuminating strange and wonderful creatures.\n\n"She thought, "Without understanding buoyancy and density, we couldn't explore these amazing places!""\n\n Fact: The Mariana Trench is so deep that Mount Everest could be submerged within it and still have over a mile of water above its peak.
Page 8
Back home, Zahra observed other examples of buoyancy. She saw a hot air balloon rising into the sky, a boat floating on the bay, and even herself floating in the swimming pool. \n\n""Buoyancy is everywhere!" she exclaimed to her mom as she watched the hot air balloon drift by."\n\n Fact: Hot air balloons float because heated air is less dense than cooler air. This difference in density creates a buoyant force that lifts the balloon.
Page 9
Her father, a calm, thoughtful, and friendly man in his 40s with glasses, a neat short beard, short dark hair with slight graying at the temples, wearing a comfortable sweater, casual trousers, and loafers, showed her a picture of an iceberg. "Even something as massive as an iceberg floats because ice is less dense than water," he explained. "But only about 10% of an iceberg is visible above the surface."\n\n"Zahra was amazed. "So, most of the iceberg is hidden underwater?""\n\n Fact: Icebergs float because ice is less dense than liquid water, a unique property due to hydrogen bonding. This allows marine life to thrive even in freezing conditions.
Page 10
Zahra smiled, understanding now why her toy submarine sank while massive ships floated. By understanding the principles of buoyancy, we can design incredible machines, explore the depths of the ocean, and even understand why icebergs float. \n\n"She realized, "Science helps us understand the world around us, from the smallest toy to the largest ship!""\n\n Fact: Understanding buoyancy allows us to design ships, submarines, hot air balloons, and even predict the behavior of icebergs, helping us navigate and explore our world more safely and efficiently.
About this story
- Location: United States
- Audience: kids (ages 6–12)
Questions and answers
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