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How Do Ships Float?

4 minutes

(Describer) An animated ball becomes an amoeba and a rocket. Title:

(singers) ♪ Science ♪

♪ Out Loud ♪♪

(Describer) A sign says HoverGroup. A cart with tires is held over a large tank of water. A man stands in the water.

If I take this box, obliterate it in the corner

(Describer) ...with a screwdriver.

and put it in the water, water rushing in will cause the box to sink.

(Describer) It does. He holds another box.

If I do the same thing to this box,

(Describer) He pokes a corner with a screwdriver.

(Describer) Then he sets it in the water.

it tips over a bit, but it still floats.

(Describer) He picks it up.

This box uses the same design that naval architects use to prevent ships a thousand times bigger from sinking. What prevents this box from sinking, even with a big hole in its side?

(Describer) On a busy dock, large containers are moved from huge ships. One ship stands behind the man.

Let's talk about why ships sink. Things less dense than water will float in water and sink if they're more dense. This ship's metal is more dense than water, so you'd think it would sink. But its shape traps a lot of air, which is less dense than water, inside it. The hull's average density is lower than the water's, so the ship floats. But if the hull springs a leak and fills with water, the density changes, and the ship sinks.

(Describer) Standing in the tank...

The design of this box prevents too much water from getting into it.

(Describer) He tears it open.

This box's hull was divided up into watertight compartments with these walls called bulkheads. When I made this hole only this compartment filled with water. The rest stayed dry and kept the box afloat. This box is subdivided and so is this ship.

(Describer) On the dock...

Say this ship is divided into ten watertight compartments. If one area got damaged, only that compartment would flood, but not the others. The added weight of the water would cause the ship to be angled in the water, but it wouldn't sink and could be taken for repairs.

(Describer) Among old model ships and plans...

Even with subdivision, why do ships still sink? It's impractical and expensive to design an unsinkable ship, especially because most of the time, ships just don't see that much damage.

(Describer) He looks at plans on a computer.

Now, naval architects try to predict the damage most likely to happen when designing ships. Ships are more complicated than this box.

(Describer) He catches it.

Naval architects have to think about where to subdivide the ship, the hull's shape, and equipment that goes into the compartments.

(Describer) With the old models...

We don't know when people started subdividing ships, but accounts of Chinese trade ships in the 5th century indicate that water entering the vessel wouldn't sink it. It's crazy that technology that existed so long ago is still being used today. Accessibility provided by the U.S. Department of Education.

(Describer) Title: Made with love at MIT.

Hello, I'm Paul. Thank you for watching Science Out Loud.

[laughs]

For more information, please visit our website.

(Describer) Title: k12videos.mit.edu. Accessibility provided by the U.S. Department of Education.

[laughter]

See what they have me do?

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The technology that keeps huge cargo ships afloat is amazingly simple. A student in Naval Construction and Engineering at MIT explains just how simple it really is. Part of the "Science Out Loud" series.

Media Details

Runtime: 4 minutes

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Episode 1
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