DENSITY

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

A. Heating an object causes the density to decrease --atoms expand and become more spread out (less tightly packed)

B. Opposite is true for cooling because atoms contract

Pressure

A.As pressure increases, the volume decreases-- atoms become more tightly packed causing density to increase

B.The opposite is true for decreasing pressure because the atoms are more loosely packed

SUMMARY

• INCREASE TEMPERATURE, DECREASE DENSITY

• DECREASE TEMPERATURE, INCREASE DENSITY

• INCREASE PRESSURE, INCREASE DENSITY

• DECREASE PRESSURE, DECREASE DENSITY

WATER

•Water is the standard used to compare the density of objects

Density of water:Density of water:

The density of waterwhen it is most dense is:

Density of water:Density of water:

Water is most dense at _______°C.

This is because water _______________ aboveand below this temperature

4°C

4expands

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!

Density of water:Density of water:

Any material with a densitygreater than water will

Any material with a densityless than water will

DENSITY FORMULA

• On the front page of the ESRT (Earth Science Reference Tables)

• Density= mass/volume• Use a scale for mass• Use lxwxh 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 cut into pieces or more is added to it, nothing happens to the density- the atoms are still packed the same

• 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- REVIEWPhases of Matter & Density- REVIEW

During which phase of matter (solid,liquid, or gas) are most materials:

A rock has a mass of 240g and a volume of 12cm³.

Showing all formulas and calculations, determine the density of the rock.

The box below has a mass of 120g.Showing all formulas and calculations,

determine the density of the box.

2.0 cm10.0 cm

2.0 cm

Density of water example: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?