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Boy, Oh Buoyancy

Boy, Oh Buoyancy. Does it Float? Does it Sink?. Things float if they are less dense than their surrounding. Helium is less dense than the surrounding air. The density of the ‘surroundings’ makes a difference!.

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Boy, Oh Buoyancy

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  1. Boy, Oh Buoyancy • Does it Float? • Does it Sink?

  2. Things float if they are less dense than their surrounding. • Helium is less dense than the surrounding air.

  3. The density of the ‘surroundings’ makes a difference! • The Dead Sea in Israel has very salty water. People can float very high with very little effort.

  4. Ships float because they have air in their hulls. However, they float at different heights in different types of water. • Salt water (The oil tanker floats high in the water.

  5. In Fresh water the same oil tanker floats lower in the water.

  6. Temperature of the surrounding water causes different densities • In cold water, ships float higher. In tropical waters, ships float lower in the water.

  7. This is a Problem!! • If a ship is loaded in a salt water port, like Japan, and then comes across the ocean to unload in a fresh water port, such as New Orleans, they could run into a serious problem if the ship was loaded too heavily at the beginning. Ships can run aground, spilling cargo or oil.

  8. Plimsoll Lines Samuel Plimsoll (1824-1898) was a member of the Brittish Parliament who was concerned with the loss of ships and crews due to overloading. He called them “coffin ships”.

  9. Plimsoll Lines • To save sailors lives, he persuaded Parliament to provide for the marking of a line on ships’ sides that would disappear below the water line if the ship was overloaded.

  10. Plimsoll Lines • T = Tropical • TF = Tropical Fresh • F = Fresh • S = Summer • W = Winter • WNA = Winter North Atlantic

  11. But the ability to float is more than density…

  12. Archimedes said…. • In order to float, the weight of the water that an object displaces must be equal to – or greater than – the weight of the object.

  13. Water is “displaced” as you enter a bathtub, but you do not float!

  14. So…. • In a pool, you spread your arms, displacing more water. The water that is displaced weighs as much or more than you do and you float!

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