Density and Pressure

Density and Pressure

1. density, p = mass / volume

2. Solids are often very dense - have a high mass for a certain volume

3. Unit: kg/m cubed

   • grams/cm cubed

4. Example: A piece of iron has a mass of 390 kg and a volume of 0.05 metres cubed. What is its density

   • 390kg / 0.05 metres cubed
     • = 7800 kg/m cubed

5. The volume of a regular object can be calculated by multiplying its length x width x height

   • Irregular: Using a displacement can and a measuring cylinder

6. Displacement:

   • Find the initial water level: 60 milliliters or 60 cm cubed
     • Put the object in the water and find the FINAL water level: 72 milliliters or 72 cm cubed
       • Volume of cylinder = Final - initial = 12 cm3

7. Pressure under a solid

   • Pressure (in Pascals) = Force (in Newtons) / Area (in square meters

8. Pressure in Liquids and Gases

9. Magdeburg Hemispheres

   • 2 large bowls put together and then pumped the air out. The bowls could not be pulled apart, even when attached two teams of horses to the bowls.

10. Pressure and Depth

    • The force at the bottom of the column is equal to all the weight of water above it. The volume (V) can be found by multiplying the area of its base (A) by the height (h) of the column.
      • The mass can be worked out by multiplying the volume by the density (p)
        • Volume = Area of Base x Height of Column
          • Mass = Volume x Density
            • Density = Mass / Volume
          • The force (F) on the bottom is equal to the weight of this volume of water = which is mass x 10
            • Pressure Difference (in Pascals) = Height (in m) x Density (in kg/m3) x g (in N/kg)
              • p = h x density x 10