DENSITY Intro to the Ocean and Atmosphere

Objectives  To how to calculate density  To predict how “high density” molecules will move  To predict how “low density” molecules will move  What factors can change density?

Take a guess…Which is more dense?  Wood or water  Ice or steam  Cold water or hot water  Metal or clay  Hot air or cold air  Freshwater or salt water  Pepsi or Coke Zero

Density Vocabulary  Density: compares the mass of an object to the amount of space it takes up  Mass: how heavy the molecules are in an object  Volume: the amount of space an object takes up  Density Current: vertical (up/down) current caused by density  Salinity: the amount of salt in a solution  Evaporation: liquid turning into a gas  Composition: what something is made of, the number of molecules inside

What is density?  Density: compares the mass of an object to the amount of space it takes up  Mass: how heavy the molecules  Density of pure water is usually 1.0 g/cm 3 More dense more molecules in a specific space, tends to sink Less dense less molecules in a specific space, tends to rise

Do Gases, Solids, and Liquids have the same density?

Why does hot air rise?  As molecules heat up, they move faster and spread out  If the molecules spread out, what happens to density?  Less density, because the same molecules take up more space  Consequence: hot air will rise (like in a hot air balloons)

Why does cold water sink?  Cold water molecules move more slowly and get closer together  Same mass taking up less volume= more dense  Cold water sinks to the bottoms

How does composition affect density?  Pure water, with no other molecules in it, is rare. Drinking water and the water in the ocean have many different types of molecules dissolved in it.  What is dissolved in the ocean water?  Salts like NaCl, gases like carbon dioxide (CO 2 ) and oxygen (O 2 ), and other things  Which is more dense, pure water or ocean water? Pure Water Density=1.0 g/cm 3 Ocean Water Density=1.025 g/cm 3 Ocean water is more dense. It has more things dissolved in it. It has a larger mass to take up the same space. The more stuff that is dissolved in the ocean, the more dense it is.

How do you calculate density? Ex1: If a cube has a mass of 25g but still has only a 5cm 3 volume, what is its density? Ex2: If a cube has a mass of 50 grams and a volume of 5 cm3, what is its density? Ex3: Which is more dense, the cube from ex1, or the cube from ex2?

Why should I care about density?  Hot water rising and cold water sinking will explain GLOBAL OCEAN CURRENTS  Hot air rising and cold air sinking will explain GLOBAL WIND PATTERNS  The interaction of rising and cooling air and water will explain GLOBAL CLIMACTIC CHANGES

On your climate map, label the oceans.

So…Which is more dense?  Wood or water  Ice or steam  Cold water or hot water  Metal or clay  Hot air or cold air  Freshwater or salt water  Pepsi or Coke Zero