Relative density
How many times denser than water.
Aluminium and water
An aluminium block has a density of 2.7 g/cm³. Water has a density of about 1 g/cm³.
How many times denser than water is aluminium?
What this lesson covers
The idea
Relative density of a substance with respect to water = Density of that substance / Density of water at that temperature; it is a number without units telling how many times denser than water it is.
Aluminium and water
An aluminium block has a density of 2.7 g/cm³. Water has a density of about 1 g/cm³.
How many times denser than water is aluminium?
- 2.7 times
- 27 times
- 1 time
Compare with water
Press Next step.
Relative density
Relative density of a substance with respect to water = density of the substance ÷ density of water at that temperature. It tells how many times denser than water the substance is. It has no units.
Relative density = Density of the substance ÷ Density of water. It has no units.
Notes
Relative density = density of substance ÷ density of water. It is a number without units.
Check yourself
Relative density has …
Relative density tells us …
A substance has a density of 3 g/cm³. Water is 1 g/cm³. What is its relative density with respect to water?
Answer: 3
3 ÷ 1 = 3. It has no units.
Aluminium has a relative density of 2.7 with respect to water. It is …
- units of kg. It is a ratio, so it has no units.
- units of g/cm³. It is a ratio of two densities, so the units cancel.
- no units — correct. Yes!
- how many times denser than water a substance is — correct. Yes!
- the colour of the substance. It tells how many times denser than water.
- the temperature. It compares density with that of water.
- 2.7 times lighter than water. Greater than 1 means denser than water.
- 2.7 times denser than water — correct. Yes!
- equal to water. Water would have a relative density of 1.