Buoyancy Lesson for Kids

Instructor: Tammie Mihet

Tammie has taught elementary school for 14 yrs. and holds an MA in Instructional Technology

Have you ever wondered how battleships, also known as megaships, float on water? How can something that weighs 2,000 tons stay afloat! In this lesson find out what buoyancy is and what affects it.


Have you ever thought about why some things float on water while other things sink? Think about throwing a pebble in the water, does it sink or float? How about throwing a basketball in the water, does it sink or float? Little pebbles sink while a giant basketball floats, but why is that? The secret is buoyancy, or the ability of objects to float in water or air. Whether or not an object has buoyancy depends mostly on two factors: the amount of water an object displaces and the density of an object. A pebble is dense and displaces very little water, therefore it sinks. However, a basketball is not very dense and displaces more water, therefore it floats. Let's use the building of megaships to help us truly understand the idea of buoyancy!

A Basketball Floats and a Pebble Sinks

Floating Megaships

Have you ever seen a U.S battleship? They are huge mini-cities that carry thousands of military soldiers, weapons, even airplanes, and all the supplies needed to live on sea for long periods of time. How do these megaships stay afloat? As the battleship is placed in the water, it begins to sink down into the water. As the boat sinks, it begins to move the water underneath it, or displaces it, causing the water to rise up on the side of it. The further the ship is submerged into water the more pressure, or upward force, the water applies on it. The ship will continue to sink into the water until the weight of the water that the sinking ship displaces is equal to the weight of the ship. But, this isn't all that needs to be taken into account to make those mega ships float!

The US Battleship Missouri
US Battleship

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