Two more compound measures: density (mass per volume) and pressure (force per area), with unit changes and mixtures.
What you will learn
- Use density = mass ÷ volume
- Use pressure = force ÷ area
- Change compound units
- Find the density of a mixture
Density and pressure
density = mass ÷ volume
pressure = force ÷ area
A 300 g block with volume 120 cm³ has density 300 ÷ 120 = 2.5 g/cm³. A 600 N crate on 0.2 m² presses with 600 ÷ 0.2 = 3000 N/m². A smaller area gives a bigger pressure: the same force on a smaller area presses harder. To compare, work out force ÷ area for each area, or just pick the smallest area.
Each formula can be turned round, just like speed = distance ÷ time:
mass = density × volume volume = mass ÷ density
force = pressure × area area = force ÷ pressure
A pebble of mass 52 g and density 2.6 g/cm³ has volume 52 ÷ 2.6 = 20 cm³.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Density and pressure
- Other rates
- Mixtures and units
7 practice questions, marked as you go; about 20 minutes in all.
Key terms
Rate
In this unit: Rates, compound measures and growth
Speed, density and pressure, rates of change read from graphs, compound interest and depreciation, and exponential growth and decay.