How do we know?
↻ One of the pages with a moving picture
A famous story about a king’s crown, and a lot of doubt about it.
- Water pushes up on anything in it. This upward push is called buoyancy.
- As an object goes in, it shoves water out of the way. The more water it moves aside, the bigger the push up.
- If the push up matches the object’s weight before it’s all the way under, it floats. If not, it sinks.
- A steel ship is hollow and wide, so it moves lots of water aside and stays up.
Shape matters as much as weight. A cube of solid iron, one foot on each side, weighs 491 pounds and sinks like a stone. Shape the same iron into a big bowl, and it floats!
We know the story of Archimedes and the king’s gold crown from Vitruvius, a Roman writer who told it long after Archimedes lived. Later scientists, like Galileo, doubted parts of it.
Salty water pushes up harder. The Dead Sea is so salty and heavy that people float without even trying.
Wow number
491 pounds of solid iron, in a cube one foot on each side, sinks like a stone. Shape the same iron into a big bowl, and it floats!
Myth or fact?
Heavy things always sink. Myth. A huge steel ship floats because of its shape.
Ice floats on water. Fact. Ice is less dense than liquid water.
Think about it
Why do you think it’s easier to float in the salty sea than in a swimming pool?
Where in the world?
Syracuse, Sicily, Italy where the story goes that the thinker Archimedes solved a puzzle about a king’s gold crown, over 2,000 years ago. The water of the Dead Sea in the Middle East is so salty and heavy that people float without even trying — 37.0755° N, 15.2866° E.
Where these facts come from
Every number on page 44, and who measured it
This page tells us how much a cubic foot of pure iron weighs.
Density of Iron and Iron Alloys — AmesWeb, an engineering reference website
amesweb.info/Materials/Density_of_Iron.aspx
We checked it on 31 October 2026
This page explains buoyancy and why an iron bowl floats when an iron block sinks.
Transportation and Ship Design — The University of Hawaiʻi
manoa.hawaii.edu/exploringourfluidearth/physical/navigation-and-transportation/transportation-and-ship-design
We checked it on 31 October 2026
This page tells the story of Archimedes and the king's golden crown, and why people doubt parts of it.
The Golden Crown (Introduction) — A math professor's Archimedes pages at New York University
math.nyu.edu/Archimedes/Crown/CrownIntro.html
We checked it on 31 October 2026
This page tells us how easy it is to float in the Dead Sea.
JetStream Max: "A Funny Bath" — NOAA, the U.S. weather and ocean agency
noaa.gov/jetstream/dead-max
We checked it on 31 October 2026
This page shows people floating high in the Dead Sea.
Photos: Floating high in highly saline water. USGS Water Science School — The U.S. Geological Survey, the government's Earth scientists
water.usgs.gov/edu/gallery/dead-sea-floating.html
We checked it on 31 October 2026
This is the crown story as Vitruvius wrote it, over 2,000 years ago.
The Golden Crown (Sources) — A math professor's Archimedes pages at New York University
math.nyu.edu/Archimedes/Crown/Vitruvius.html
We checked it on 31 October 2026
This page tells us why ice floats.
Water Density — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/water-science-school/science/water-density
We checked it on 5 November 2026
This page has a build-a-boat activity like our Try it!
Build a boat — NOAA, the U.S. weather and ocean agency
noaa.gov/office-education/outreach-communication/hands-on-science-activities/build-a-boat
We checked it on 31 October 2026
Has this changed?
Why things float or sink is not going to change.
Parts of the crown story may never be proven, and people still debate it.
Words from this page
- buoyancy
- The upward push that water gives to anything in it.
- dense
- Heavy for its size. Something less dense than the water around it will float.
Try it!
Build a foil boat that floats.
1. Take two same-size squares of aluminum foil. 2. Squeeze one into a tight ball. Fold the other into a flat boat with sides. 3. Put both in a bowl of water. Add pennies to the boat, one at a time.
What happens: the ball sinks, but the boat floats and holds pennies. Its wide shape moves more water aside!
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