Bellringer 9-14-09

Calculate the following

9.0 x 1023 - 9.0 x 1021

DENSITYMass vs volume

Thought question

Which is heavier a pound of lead or a pound of feathers?

Most people say lead…

They are thinking about if you have the same size piece of lead and feathers obviously the lead will be heavier.

However, a pound of lead is much smaller in size than a pound of feathers

Why?

The answer is density

Lead atoms are packed tightly together Feathers are not

Density is…

The ratio of the mass of an object to its volume

Density = mass/volume A 10.0 cm3 piece of lead has a mass of

114 g. How would you find density? Density of lead is 11.4 g/cm3

Density

As mass increases, density increases As volume increases, density decreases Depends only on substance not on size

A block of maple wood with a volume of 405 cubic centimeters and a density of 0.67 g/cm3 is sawed in half. The density of the two smaller blocks is now --

A one-fourth the original densityB one-half the original densityC two times the original densityD the same as the original density

Densities of common materials

Can you find any themes?

Water is 1 g/cm3

Density Trends

Solids usually most dense Gases usually least dense Exception is water

Ice is less dense than liquid waterWater expands as it freezes and creates air

pocketsVolume increases and mass remains

constant, therefore density decreases

Floating is related to density A substance that is less dense will float

in a substance that is more dense Example…

Helium density 0.166 g/L Air density 1.2 g/LWater density 1 g/cm3 Oil density 0.922 g/cm3

Ice density 0.917 g/cm3

Steel density approx. 8 g/cm3

What about ships?

Calculations What is the density of a piece of wood

that has a mass of 25.0 grams and a volume of 29.4 cm3?

D=m/v m=25.0 g v=29.4 cm3

25.0 / 29.4 D = 0.850 g/cm3

A  piece of wood that measures 3.0 cm by  6.0 cm by 4.0 cm has a mass of 80.0 grams. What is the density of the wood? Would the piece of wood float in water?

D = 1.1 g/cm3

The density of aluminum is 2.70 g/mL. If the mass of a piece of aluminum is 244 grams, what is the volume of the aluminum?

Use the triangle Cover up what you are looking for It will tell you math to do V=m/D V = 90.4 mL

Water displacement

Silly putty with a mass of 8.0 g is placed in a graduated cylinder with an initial water level of 25 ml After placing silly putty into graduated cylinder the water level rose to 29 ml. What is the density of the silly putty?

29 ml – 25 ml = 4 ml D = 8 g / 4 ml D = 2 g/ml