Mass, Weight & Density

• Mass

  A measure of the quantity of matter in an object at rest relative to the observer
• Define weight in terms of the effect of a gravitational field

  The effect of a gravitational field on object with mass
• Gravitational field strength

  The force per unit mass acting on an object in a gravitational field
• What is the purpose of using a balance?

  To compare the weights of two objects or to measure the mass of an object
• How is weight affected by the gravitational field strength?

  The stronger the gravitational field, the greater the weight of the object
• Density

  The mass per unit volume of a material
• Volume

  The amount of space occupied by an object in three-dimensional space
• What are the factors affecting whether an object sinks or floats?

  Upthrust and density
• State the condition for liquid A to float on liquid B

  Liquid A will float on top of liquid B if the density of liquid A is lower than that of liquid B
• How do you determine the density for a liquid?

  • Measure the mass of an empty container
  • Pour the liquid into the container and measure the combined mass of the container and the liquid
  • Calculate the mass of the liquid by subtracting the mass of the empty container from the combined mass
  • Measure the volume of the liquid using a graduated cylinder
  • Divide the mass of the liquid by its volume to get the density
• How do you measure the volume of a regularly shaped solid?

  • Measure the mass of the solid using a balance
  • Measure the dimensions of the solid (lwh) using a ruler
  • Calculate the volume of the solid by multiplying its length, width, and height
  • Divide the mass of the solid by its volume to get the density
• How do you measure density of an irregularly shaped solid

  • Fill a cylinder with a liquid until it's partially full, and note the initial volume of the liquid
  • Carefully lower the irregularly shaped solid into the cylinder, make sure it's fully submerged
  • Note the final volume of the liquid, accounting for any rise in the liquid level
  • The difference between the final and initial volumes gives the volume of the irregular solid displaced by the liquid
  • Measure the mass of the irregular solid using a balance
  • Divide the mass of the irregular solid by the volume of liquid displaced to get its density