Density

What is density?

Definition: It is defined as the mass per unit volume.

Classic Density Question:

1. 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.

2a. Describe how you would measure the volume of a piece of a 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.

2b. 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.

3. 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.

4. Why does a heavy steel ship float on water?

• A large ship is an object that is made up of more than one material.
• In addition to steel, it contains a large volume of air in the various rooms and cabins.
• Therefore, we will have to consider the average density of the ship.
• The average density of the ship is actually less than the density of seawater.
• Therefore, the ship is able to float!