DENSITY Mark Place, 2009-2010 www.LearnEarthScience.com

DENSITY: The mass of a substance per unit of volume DEFNITION DENSITY: The mass of a substance per unit of volume In simple terms…How much “stuff” is in a certain amount of space Weight/amt of space taken up

Only way to change density is by changing the temperature or pressure

Opposite is true for cooling-> atoms contract Heating an object causes the density to decrease --atoms become less tightly packed Opposite is true for cooling-> atoms contract Density

Density density temperature

Pressure As pressure increases, the volume decreases causing higher density As pressure decreases, volume increases causing lower density

SUMMARY INCREASE TEMPERATURE, DECREASE DENSITY DECREASE TEMPERATURE, INCREASE DENSITY INCREASE PRESSURE, INCREASE DENSITY DECREASE PRESSURE, DECREASE DENSITY

Water is the standard used to compare the density of objects

The density of water when it is most dense is: Density of water: 1.00 g/mL

4 expands Density of water: Water is most dense at _______°C. This is because water _______________ above and below this temperature expands 4°C

THE DENSITY EXCEPTION Usually, solids are the most dense and gases are the least dense (think of Earth layers) When water freezes into ice, the atoms expand become less packed As a result, ice is less dense than water

THIS IS WHY ICE CUBES FLOAT IN WATER!

Any material with a density less than water will Density of water: Float or Sink Any material with a density less than water will Any material with a density greater than water will FLOAT SINK

DENSITY FORMULA On the front page of the ESRT (Earth Science Reference Tables) Density= mass/volume Use a scale for mass V= l*w*h for regular solids Use cylinder and displacement method for irregular solids Units: g/cm3 for reg. solids; g/mL for irreg. objects

If substance is broken or more is added to it, nothing happens to the density (the atoms are still packed the same) Density

Example 1: the density of a gallon of water is 1. 0 g/mL Example 1: the density of a gallon of water is 1.0 g/mL. the density of a glass of water is also 1.0 g/mL Example 2: a wood block cut in half has the same density as the original wooden block

Phases of Matter & Density- REVIEW During which phase of matter (solid, liquid, or gas) are most materials: most dense? least dense? solid gas

Sample Problems density = mass / volume = 240g / 12cm³ page 7 A rock has a mass of 240g and a volume of 12cm³. Showing all formulas and calculations, determine the density of the rock. Sample Problems density = mass / volume = 240g / 12cm³ page 7 = 20.0 g/cm³

Sample Problems density = mass / volume = 120g / 40cm³ page 7 The box below has a mass of 120g. Showing all formulas and calculations, determine the density of the box. volume = L x W x H Sample Problems 2.0 cm = 2.0cm x 2.0cm x 10.0cm 10.0 cm 2.0 cm = 40.0 cm³ density = mass / volume = 120g / 40cm³ page 7 = 3.0 g/cm³

D = m ÷ v = 25g ÷ 50mL = 0.5 g/mL Density of water example: If an object has a mass of 25g and a volume of 50mL, will it sink or float in liquid water? D = m ÷ v = 25g ÷ 50mL = 0.5 g/mL it will FLOAT

Video Watch the following video. While you’re watching the video, write down at least 3 things in your notes that you find important, interesting, or helpful in remembering the concepts presented. https://www.youtube.com/watch?v=ABsVP41-EeY