density

• Matter


  Sub-atomic particles and anything made from them, such as atoms and molecules
• Solid


  • Particles are tightly packed in a regular structure
• Liquid


  • Particles are tightly packed but free to move past each other
• Gas


  • Particles are spread out and move randomly
• There is little difference between the density of a liquid and its corresponding solid (eg water and ice)
• The same mass takes up a bigger volume in a gas, meaning the gas is less dense
• Density also depends on the material
• Density


  A measure of compactness and the ratio of mass to volume, usually measured in kg/m³ or g/cm³
• 1 g/cm³ is equal to 1,000 kg/m³
• Densities


  • Aluminium (2.7 g/cm³ or 2,700 kg/m³)
  • Lead (11.6 g/cm³ or 11,600 kg/m³)
  • Iron (7.9 g/cm³ or 7,900 kg/m³)
• Matter is made up of small particles called atoms
• Atoms can exist on their own or together as molecules
• Atoms are very small and around 100,000,000 of them end to end would measure 1 centimetre
• Density


  A measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m 3 ) or grams per centimetre cubed (g/cm 3 )
• Volume


  The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml
• Calculating volume of regular shapes


  1. Cube: length (l), width (w), height (h) - volume = lwh

  2. Sphere: diameter (d) - volume = (4/3)π(d/2)^3

  3. Cylinder: diameter of base (d), length of cylinder (l) - volume = π(d/2)^2l

  4. Cone: diameter of base (d), length of cylinder (l) - volume = π(d/2)^2(l/3)
• Irregular shape


  A shape with unequal side lengths
• Measuring volume of irregular shapes

  1. Use a displacement can filled with water above a narrow spout

  2. Place the irregular object in the can, the displaced water comes out of the spout and is collected in a measuring cylinder

  3. The volume of the displaced water is equal to the volume of the object
• The displaced water in the cylinder occupies the same amount of space as the object in the can, which means that their volumes are the same
• Matter is made up of small particles called atoms. Atoms can exist on their own or together as molecules.
• Atoms are very small and around 100,000,000 of them end to end would measure 1 centimetre.
• Density


  The mass per unit volume of a substance
• Investigating density experiment


  1. Record the mass accurately

  2. Measure and observe the mass and the volume of the different objects

  3. Use appropriate apparatus and methods to measure volume and mass
• Method 1: Regular solids

  1. Use a ruler to measure the length (l), width (w) and height (h) of a steel cube

  2. Place the steel cube on the top pan balance and measure its mass

  3. Calculate the volume of the cube using (l × w × h)

  4. Use the measurements to calculate the density of the metal

  5. Use vernier callipers to measure the diameter of the sphere

  6. Place the metal sphere on the top pan balance and measure its mass

  7. Calculate the volume of the sphere using (4/3) π (d/2)^3

  8. Use the measurements to calculate the density of the metal
• Method 2: Stone or other irregular shaped object


  1. Place the stone on the top pan balance and measure its mass

  2. Fill the displacement can until the water is level with the bottom of the pipe

  3. Place a measuring cylinder under the pipe ready to collect the displaced water

  4. Carefully drop the stone into the can and wait until no more water runs into the cylinder

  5. Measure the volume of the displaced water

  6. Use the measurements to calculate the density of the stone
• Method 3: Water (or any liquid)


  1. Place the measuring cylinder on the top pan balance and measure its mass

  2. Pour 50 cm3 of water into the measuring cylinder and measure its new mass

  3. Subtract the mass in step 1 from the mass in step 2. This is the mass of 50 cm3 of water

  4. Use the measurements to calculate the density of the water
• Object


  • Steel cube
  • Steel sphere
  • Stone
  • Water
• Density


  Mass ÷ Volume
• Densities calculated from measurements are subject to experimental error.
• The experiment shows steel to have two different values for density: 7.8 g/cm3 and 7.9 g/cm3. This may be because some measurements are taken to different numbers of significant figures and this can create rounding errors, so the last significant figures differ. But it can also mean that the actual value is between 7.8 g/cm3 and 7.9 g/cm3.
• Control measures


  • Use a measuring cylinder to collect displaced water and prevent spills