density and pressure

• density = mass/volume
• pressure = force/area
• determining the density of a regular shaped solid:

  1. measure the length, width and height of it using a ruler
  2. measure the mass of the object using weighing scales
  3. calculate volume (l x w x h)
  4. apply formula density = mass/volume
• determining density of an irregular shaped solid:

  1. measure object's mass on a weighing scale
  2. fill eureka can with water until water is level with bottom of the pipe
  3. place measuring cylinder under pipe to collect displaced water
  4. drop object into can and wait until no more water flows into cylinder
  5. measure volume of displaced water
  6. apply formula density = mass/volume
• measuring density of a liquid:

  1. measure mass of measuring cylinder
  2. pour 100cm3 liquid into the measuring cylinder
  3. measure new mass
  4. subtract mass of empty cylinder from mass of cylinder + liquid (this is the mass of the liquid)
  5. apply formula density = mass/volume
• to calculate pressure we need to know

  • force or weight exerted
  • surface area over which the force is spread
• units for pressure = Pascals (Pa)
• force/area = N/m2 = Pa
• gas pressure is caused when gas particles hit the walls of their container
• the more often gas particles hit the walls of their container, the faster they are moving when they do this, the higher the pressure
• when particles in a gas collide with eachother and the walls of their container kinetic energy is conserved in the collisions
• the particles in a gas are in a constant state of random motion
• when particles collide with the walls of the container that holds them they exert a force
• pressure in gases give us a measure of the force per unit area on the container walls. (adding up all the individual forces of the particles hitting the walls - for the force - and dividing by the area of the container is how pressure in gases is calculated)
• if a gas particle is moving faster it will hit the container wall harder and exert a larger force
• higher frequency of collisions = higher pressure
• units for density


  kg/m3

  g/cm3
• pressure


   the ​amount of force per unit area​.