Purpose of practical activity Density is an important concept − it is a measurement that compares the amount of mass that an object has to its volume. This means that we can compare different materials in terms of how dense they are. Density indicates whether a solid will float or sink. To find the density of a material we need to know its mass and its volume. This experiment will enable you to see how this is done and relate it to whether the material floats or sinks. Learning outcomes
Maths skills required
To understand how the volumes of regular and irregular objects can be determined.
Take and record readings.
To calculate density and relate this to whether a material floats or sinks in water. To understand how density can explain buoyancy.
Formulae
Perform mathematical operations, including multiplication and division.
density =
mass volume
Analyse data, spotting trends and patterns. Finding volumes of cuboids.
Set up Apparatus list Various solid objects made of different materials; some should float in water and some should not. There should also be a variety of regular and irregular shapes.
Rulers
Electronic balances
Displacement cans or beakers and measuring cylinders
Cotton thread or string or fishing line
Safety notes Do not handle any mains electric sockets, switches or plugs with wet hands. Wipe up any water spilt on the floor to avoid slipping and falling. Common mistakes and how to avoid them Remember that density is calculated from mass divided by volume – not the other way around. When lowering an irregular object into water to find its volume, take care to capture every drop of water that overflows. We are working with values of density in g/cm3, so the mass has to be in grams and the volume in cm3.
Method Read these instructions carefully before you start work. 1.
Sort out the objects you are going to be using in your investigation. Separate them into regular and irregular objects. Make sure you have at least one of each.
2.
For each object, use the balance to determine its mass and record this in the table.
3.
If the object has a regular shape, use the correct formula to find the volume. For example, if it is a cuboid, volume will be length times width times height. Record this data in the table.
Physics 3
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