C4.1: Density Physical Science. C4.1 Density Supplies: A pencil and science notebook Standards: – 8a) Density is mass per unit volume – 8b) Calculate.

C4.1: Density

Physical Science

C4.1 Density

• Supplies: A pencil and science notebook• Standards: – 8a) Density is mass per unit volume– 8b) Calculate the density of substances from

measurements of mass and volume– 9f) Apply simple mathematic relationships to

determine a missing quantity

C4.1 Density

• You will be taking notes using Cornell Notes format or Charting Notes format.

C4.1 Density

• Definitions• Density: the mass of matter per unit volume;

density is typically expressed in units of grams per milliliter (g/mL), grams per cubic centimeter (g/cm3), or kilograms per cubic meter (kg/m3).

Density is a property of matter

• Population density?• Forest density?• Density of stars?• Air quality?

Density in Physics• Density is a property

of matter, like color or size.

• Density is mass per unit volume.

• Given a cubic centimeter of – Steel– Water– Air

• Which has more mass?

Units of density• Units are g/cm3

• Ratio means• 1 g/cm3 = 1000 kg/m3

• Steel at 8.7 g/cm3 is 8,700 kg/m3 (multiply by 1000 and change units.)

• Oak at 600 kg/m3 is 0.60 g/cm3 (divide by 1000 and change units.)

• How does the density of oak compare to the density of water?

Solving problems

• D=m/v

• Solve for m• Solve for v

Solve it

• A stainless steel sphere has a mass of 25 grams and a volume of 3.2 cm3. What is the density of the sphere?

• A cube has a mass of 7.8 grams. The length of the sides of the cube is 1.2 cm. What is the density of the cube?

Solve it, then compare

• Honey’s density is 1.4 g/cm3

• Write this as kg/m3

• Sandstone’s density is 20,280 kg/m3

• Write this as g/cm3

• Compare answers with with someone nearby.

Density Samples

Determining Density

• Use a balance to find the mass

• Use a graduated cylinder to find the volume (not a beaker – why?)

• D = mass/volume

Using a graduated cylinder

• Read the mark at eye level

• Read volume at center of meniscus (ask your teacher!)

• 1 mL = 1 cm3

Volume of solids

• Length X width X heights gives cubic centimeters

• What is the volume of a box that is 10” long, 5” wide, and 3” high?

• What is the volume of a box that is 2’ long, 1’ wide, and 9” high?

More volumes, use 3.14 for π

• Sphere: V=(4/3)πr3

• What is the volume of a sphere with a radius of 2 cm?

• Cylinder: V=πr3h• What is the volume of a cylinder that is 10 cm

tall and has a radius of 3 cm?

Irregular shapes• Volume by displacement of

fluid• Remember: 1 mL = 1 cm3

• Fill graduates cylinder with fluid to known level (50 mL)

• Carefully slide object down the side of the cylinder

• Compute the increase in the fluid height

• 82 mL - 50 mL = 32 mL• 32 mL = 32 cm3

Compute this

• I fill a graduated cylinder with 50 mL of water.• I slip a stone into the cylinder and the water

raises to 62 mL.• What is the volume of the stone?

Why density varies• Mass of each atom or

molecule that that makes up the substance – a calcium atom has more ‘stuff’ in it than an oxygen atom.

• How tightly the atoms are packed -- the atoms are closer together in diamond that in graphite, but both are carbon.

• (Except for water) solids are more dense than liquids

• Liquids are more dense than gases

Ticket Out: Answer this

• Which has more mass, a pound of bricks or a pound of feathers?

• Which is more dense, a pound of bricks or a pound of feathers.