  ## Section 5 Density and pressure

Notes
Step 1

List all the information in symbol form and change into appropriate and consistent SI units if required.

l=10.0cm

w=2.0cm

h=5.0cm

m=80g

ρ=?

Step 2

Use the correct equations.

 V = l × w × h and ρ = m  V

Step 3

Calculate the answer by putting the numbers into the equations.

 ρ = m  V = 80  100 = 0.80g/cm3 (2 sig. figs)

ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.

The unit g/cm3 is acceptable for density, although the SI unit is kg/m3. This is why cm has not been converted into m in the above calculation.

## Determining the density of a liquid

• A measuring cylinder is used to measure the volume of a liquid. Volume must be measured to the bottom of the meniscus (the bottom of the curved surface of the liquid). • When using a measuring cylinder, be careful to avoid parallax error (see pages 2-3). If the volume is not measured at right angles to the meniscus, parallax error will cause incorrect high or low measurements.