Contents
Key Stage 3
Meaning
Density is the amount of mass per unit volume of an object.
About Density
- The units of density are kg/m3.
- An object with a large amount of mass in a small volume is said to have a high density.
- An object with a small amount of mass spread over a large volume is said to have a low density.
Solids are the most dense state of matter because there are a large number of particles in a certain volume and gases are the least dense state of matter because there are a small number of particles in a the same volume. |
Density and Floating
- If an object is more dense than water it will sink.
- If an object is less dense than water it will rise through water and float on the surface.
Equation
- Density = Mass/volume
\[\rho = \frac{m}{V}\] Where:
Example Calculations
5000kg of Iron has a volume of 0.635m3. Calculate the density of Iron. | A 50,000cm3 container of water is full with a 50kg mass of water. Calculate the density of water. | A 200,000cm3 volume of air has a mass of 245g. Calculate the density of air. |
Volume = 0.635m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{5000}{0.635}\] \[\rho = 7874kg/m^3\] |
Volume = 50,000cm3 = 0.05m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{50}{0.05}\] \[\rho = 1000kg/m^3\] |
Volume = 200,000cm3 = 0.2m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{0.245}{0.2}\] \[\rho = 1.225kg/m^3\] |
Key Stage 4
Meaning
Density is the amount of mass per unit volume of an object.
About Density
- The SI Unit of density is kg/m3.
- An object with a large amount of mass in a small volume is said to have a high density.
- An object with a small amount of mass spread over a large volume is said to have a low density.
Finding the Density
Finding The Density of a Regular Object
- Measure the mass of the cuboid using an Electronic Balance or Measuring Scale.
- Measure the length, width and height of the cuboid.
- Multiply the length, width and height to calculate the volume.
- Divide the mass by the volume of the cuboid to calculate the density.
Finding The Density of an Irregular Object
- Measure the mass of the object using an Electronic Balance or Measuring Scale.
- Fill a measuring cylinder with enough water to submerse the object.
- Take a reading of the volume of water in the Measuring Cylinder.
- Place the object in the Measuring Cylinder and ensure it is submersed.
- Take a reading of the volume of water + object in the Measuring Cylinder.
- Subtract the volume of water from the volume of water + object to find the volume of the object.
- Divide the mass by the volume of the object to calculate the density.
Solids are the most dense state of matter because they have the largest amount of matter per unit volume and gases are the least dense state of matter because they have the smallest amount of matter per unit volume. |
Density and Floating
- If an object is more dense than water it will sink.
- If an object is less dense than water it will rise through water and float on the surface.
Equation
- Density = Mass/volume
\[\rho = \frac{m}{V}\] Where:
Example Calculations
5000kg of Iron has a volume of 0.635m3. Calculate the density of Iron correct to two significant figures. | A 50,000cm3 container of water is full with a 50kg mass of water. Calculate the density of water correct to two significant figures. | A 200,000cm3 volume of air has a mass of 245g. Calculate the density of air correct to two significant figures. |
Volume = 0.635m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{5000}{0.635}\] \[\rho = 7874kg/m^3\] \[\rho \approx 7900kg/m^3\] |
Volume = 50,000cm3 = 0.05m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{50}{0.05}\] \[\rho = 1000kg/m^3\] |
Volume = 200,000cm3 = 0.2m3 \[\rho = \frac{m}{V}\] \[\rho = \frac{0.245}{0.2}\] \[\rho = 1.225kg/m^3\] \[\rho \approx 1.2kg/m^3\] |