Chapter 4 - Mass, Weight and Density

1.

Explain why a beam balance will give the same value of mass at different places for the same object.

  • Bean balance measures the mass of the object and mass is constant and does not change from place to place.

 2.

Explain why a spring balance may give different readings at different places when weighing the same object.

  • Spring balance measures the weight of an object which depends on the different gravitational field strength at different places (usual referring to different planets).

 3.

Distinguish between mass and inertia. State how they are related to each other.

  • Mass is the measure of amount of matter in a body.
  • Inertia refers to the reluctance of a body to change its state of motion.
  • The inertia of an object increases with its mass.

4.    Describe how you would find the density of a small stone with irregular shape.

  • Place a certain volume of water in a measuring cylinder and record the volume, V1.
  • Lower the stone into the measuring cylinder of water with a string until it is fully submerged and record the new volume, V2.
  • The volume of the stone, V is given by V2 – V1.
  • Measure the mass of the stone, m, using an electronic balance.
  • The density of the stone can be calculated using the formula, density = mass / volume.

 5.

Describe how you would measure the volume of a piece of floating object by means of a measuring cylinder, a thread, a sinker, and water.

  • Lower a sinker into a measuring cylinder containing some water until it is fully submerged and records the volume, V1.
  • Attach the floating object to the sinker and lower both into the cylinder again and note the volume, V2.
  • The volume V of the floating object is given by V2 – V1.

State two precautions that should be taken when using the measuring cylinder.

  • The measuring cylinder should be placed on a flat surface when reading the volume.
  • The volume of the liquid should be read from the base of the meniscus.

 6.

Describe an experiment to find the density of a liquid. State how the measurements are taken, and show how the final results are calculated.

  • Find the mass of a clean dry beaker, m1, using an electronic balance.
  • Pour a volume, V, of the liquid from a burette (or pipette) into the beaker.
  • Find the mass of the beaker and liquid, m2, using an electronic balance.
  • The mass of the liquid m is given by m1 - m2.
  • The density of the liquid can be calculated using the formula, density = mass / volume.