How Do Boats Float?

A boat is able to float based on the amount of water it displaces or moves out of the way. When a boat pushes against the water, the water pushes back with an equal amount of force. Therefore, a wider boat is able to carry a heavier load than a long, narrow boat. Wider boats displace more water and therefore are held up by a greater water force, enabling them to carry heavier loads.

In this activity students will experiment with how much weight a boat can hold depending on the size of the boat.


Large pan with water
Toy boats (various sizes)
Pennies (or other coins)


  1. Place the boat in the water. Allow students to interact with the boat, seeing that it floats when placed in the water.
  2. Add pennies to the boat, counting how many are added before the boat sinks.
  3. Repeat this with each type of boat and compare how the boats differ in size, shape, and the amount of pennies they can hold.

Discussion Questions to Ask:

  • What did the boats do when placed in the water?
  • How many pennies do you think each boat can hold? Which boat held more pennies?
  • If you had to make a boat to carry a heavy load, what shape and size boat would you make?

When teaching concepts related to density, it is best practice to allow students to experiment with different shapes and sizes of objects. Encourage students to explore how long objects can float before sinking, or how long it takes an object to sink when placed in the water. Finding ways to connect the activity to the students’ current interests is a great way to keep young students especially interested in the topic. Additionally, finding ways that this activity relates to the real-world is a great way to extend the science learning beyond the classroom. Looking at how large ships carry cargo, or how small ships can zip through the water very quickly, are easy ways to show how this lesson of buoyancy is applied in everyday life. For more fun buoyancy teaching tips, visit:

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Automaton: Elementary Science of The Old-Fashioned Robot

This month’s Elementary Science feature is about the very early example in science history of what today we call a sophisticated robot.   An Automaton is basically an old-fashioned robot, or a “non-electronic moving machine “. Merriam-Webster’s dictionary describes one as:
1. a mechanism that is relatively self-operating; especially : robot
2. a machine or control mechanism designed to follow automatically a predetermined sequence of operations or respond to encoded instructions
3. an individual who acts in a mechanical fashion
This photo above from Wikipedia is a beautiful Japanese Tea Making Automaton.

In Jan., 2012, CBS Sunday morning produced a VERY COOL short video clip of Charles Penniman demonstrating Maillardet’s Automaton today home at The Franklin Institute Museum in Philadelphia.  Also known as the “Draughtsman-Writer”, this Automaton was built by Henri Maillardet, a Swiss clock mechanic who worked in London producing clocks and other mechanisms around the year 1800. After going through 2 fires, it eventually was found and donated to the Institute in November of 1928, after which a number of mechanics specialists worked diligently at its restoration. Compared to other old-fashioned mechanical robots through our scientific history, the Maillardet Automaton has the largest “memory”, including the ability to construct with its mechanical pen – 4 drawings and 3 quite lovely poems in both French and English languages. The Franklin Institute explains that his robot doll, as it is sometimes named, was humankind’s “…effort to imitate a living being by mechanical means…intersecting art and science…”.  The Franklin Institute homes objects of invention that tell the history of science and technology, such as Flight, Computing, Electricity, Photography and Instrumentation.

The Maillardet Automaton was a principal inspiration for Brian Selznick’s book, The Invention of Hugo Cabret. His book was later in 2001 turned into Hugo, a 2001 film directed by Martin Scorsese, starring Asa Butterfield, Hugo is a PG film produced in 2011 about the story of the first automaton. Set in 1930`s Paris, an orphan named Hugo lives in the walls of a train station and is wrapped up in a mystery involving his late father and an automaton. He finds a friend (Asa Butterfield) who helps him solve the puzzle.

This photo is of a Swiss Made Automaton in CIMA museum (Centre International de la Mécanique d’Art).  There is also historical evidence of a very early example of an automaton from ancient China, from the text Lie Zi in 3rd Century BC; and an even earlier meeting and dialogue between King Mu of Zhou (1023-957 BC) and a mechanical engineer known as Yan Shi, noted as an “artificer. The text accounts Yan Shi proudly presenting The King with a life-size, human-shaped figure of his handmade automaton:

The king stared at the figure in astonishment. It walked with rapid strides, moving its head up and down, so that anyone would have taken it for a live human being. The artificer touched its chin, and it began singing, perfectly in tune. He touched its hand, and it began posturing, keeping perfect time…As the performance was drawing to an end, the robot winked its eye and made advances to the ladies in attendance, whereupon the king became incensed and would have had Yen Shih executed on the spot had not the latter, in mortal fear, instantly taken the robot to pieces to let him see what it really was. And, indeed, it turned out to be only a construction of leather, wood, glue and lacquer, variously colored white, black, red and blue. Examining it closely, the king found all the internal organs complete—liver, gall, heart, lungs, spleen, kidneys, stomach and intestines; and over these again, muscles, bones and limbs with their joints, skin, teeth and hair, all of them artificial…The king tried the effect of taking away the heart, and found that the mouth could no longer speak; he took away the liver and the eyes could no longer see; he took away the kidneys and the legs lost their power of locomotion. The king was delighted. (Needham, Joseph; Science and Civilization in China: Volume 2. Cambridge University Press; 1986)

Another very simplified example of an automaton is that of a cuckoo clock. Once activated, the cuckoo comes out every hour and sounds “cuckoo…cuckoo”. Here is a short video from “How it is Made” showing how a cuckoo clock is made:
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