King Hieron II of Syracuse asked the Greek scientist and mathematician, Archimedes to solve a problem for him. He suspected that a craftsman had made his crown out of silver and gold, rather than all gold as he had requested. He asked Archimedes to find out if the craftsman had cheated him by using cheap materials.
Archimedes found the solution while sitting in his bathtub. He noticed that when he sat in the tub, water ran over the edge of the tub. He realized whenever any object is dropped in water, the object displaces the water, causing the water to rise or spill out of the way. The volume of water displaced is always equal to the volume of the object. Legend has it that he ran through the streets naked, shouting, “Eureka, eureka, I’ve got it!” To solve the King’s riddle, Archimedes weighed a bar of gold, a bar of silver, and the crown. He then dropped each item into the water and measured the volume of the water displaced. He found that the gold displaced the most water; the silver, the least. The crown was in the middle, proving that it was – as the King feared – part silver and part gold!
- Archimedes had discovered the laws of buoyancy, known as The Archimedes Principle. Items that float must weigh less than the fluid or gas they’re floating in; heavier items sink.
- Drop a rock into a stream and it immediately sinks. The water around the rock is buoyed up by the displaced water, but it is too heavy to float.
- Drop a rock into the ocean and the displaced will buoy it up initially, slowing it down. Eventually gravity will pull it to the bottom though.
- Try floating different objects to determine their buoyancy. Low-density objects, such as wood, cork, or a sponge, float very well. Heavy, high-density objects will likely sink. What happens when objects become waterlogged?
- Buoyancy: The power of a fluid or gas to exert an upward force (displacement) on an object placed on it.
- Volume: The amount of three-dimensional space in an object.
Visit Indiana Public Media to conduct your own Archimedes experiment. Clothing required!
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Declan, Tobin. " Fun Buoyancy Facts for Kids ." Easy Science for Kids, May 2018. Web. 26 May 2018. < http://easyscienceforkids.com/buoyancy/ >.
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