International GCSE Physics - Section 5 Density and pressure

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=

V	=	l × w × h and
ρ	=	m V

Step 3

Calculate the answer by putting the numbers into the equations.

V=l × w × h=10.0 × 2.0 × 5.0=100cm³

ρ=

100

= 0.80g/cm³ (to 2 sig. figs)

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.

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.