physics density

Density

The mass of a substance per unit volume.

Mass

How much matter is in an object.

Volume

How much space an object takes up.

Density formula

Mass divided by volume.

Units of density

Grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³).

Symbol for density

The Greek letter rho (ρ).

Symbol for mass

The letter m.

Symbol for volume

The letter V.

g/cm³

Grams per cubic centimeter.

kg/m³

Kilograms per cubic meter.

1 g/cm³

Equals 1000 kg/m³.

Compactness

How closely packed the particles in a substance are.

Density depends on

What the object is made of.

Density does not depend on

Size or shape of the object.

Float

When an object stays on the surface of a liquid.

Sink

When an object goes to the bottom of a liquid.

Lower density

Object floats in fluid if it has lower density than the fluid.

Higher density

Object sinks if it has higher density than the fluid.

Finding density

Measure mass and volume, then divide mass by volume.

Measuring mass

Use a balance.

Measuring volume for a box

Measure length, width, and height.

Finding volume for a box

Multiply length × width × height.

Tool to measure length

Ruler.

Finding volume for an irregular solid

Submerge it in a Eureka can filled with water.

Eureka can

A container used to find volume by water displacement.

Water displaced

Water pushed out when object is submerged.

Measuring cylinder

Tool used to collect and measure water displaced.

Volume of object

The same as the volume of water displaced.

Practical method for density

Measure mass and volume, then use the formula.

Recording volume

Write down the volume collected in the measuring cylinder.

Object's mass

Weight measured by the balance.

Object's volume

Space taken up, found by measurement or displacement.

Step 1 for density

Measure mass using a balance.

Step 2 for density

Measure volume using length × width × height, or water displacement.

Step 3 for density

Plug mass and volume into density formula.

Material example: Pine

Density about 0.5 g/cm³.

Material example: Oil

Density about 0.8 g/cm³.

Material example: Water

Density about 1.0 g/cm³.

Material example: Metal (example)

Density about 7.9 g/cm³.

Density and floating

Solid floats if density is lower than liquid's density.

Density and sinking

Solid sinks if density is higher than liquid's density.

Displaced water

The amount of water pushed out by a submerged object.

Use of Eureka can

To find the volume of an irregular object.

Submerging

Placing completely underwater.

Mass measurement

Using a balance to find how heavy an object is.

Volume measurement

Measuring how much space an object fills.

Length

How long something is.

Width

How wide something is.

Height

How tall something is.

Multiplying dimensions

Length × width × height = volume.

Appropriate measuring equipment

Ruler, measuring cylinder, Eureka can.

Compactness and density

More compact = higher density.

Low density

Particles spread out.

High density

Particles tightly packed.

Same material

Same density, no matter the size or shape.

Different material

Different density.

Average density

Total mass divided by total volume.

Mass per unit volume

Main idea of density.

Using formula for density

Mass ÷ volume = density.