Density Chapter 4 Physical Science. Tuesday, October 2, 2011 Supplies: A pencil and science notebook Standards: 8a) Density is mass per unit volume.

DensityChapter 4

Physical Science

Tuesday, October 2, 2011

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

Warm-up

Given what you know about energy in solids, liquids, and gases, how and why do you think a lava lamp works.

Agenda

Pass back homework

Density Lecture

Ticket-out

What is density

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?

Write it

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?

Density is a ratio

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?

Solve it, them 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.