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/cm3

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 (CO2) and

oxygen (O2), and other things Which is more dense, pure water or ocean water?

Pure Water

Density=1.0 g/cm3

Ocean Water

Density=1.025 g/cm3

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 5cm3 volume, what is its

density?

)(cm Volume

(grams) Mass Density

3

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