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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