Materials Detectives

AIM:

To investigate the properties of different materials

CURRICULUM LINK:

KS2: Sc3 Materials and their Properties, Grouping and Classifying Materials. 1(a) - (c)
KS1: Sc3 Materials and their Properties, Grouping Materials. 1(c) and (d)

TIME:

40 minutes. 30-35 minutes to investigate materials, 5-10 minutes to solve crime. Start each group on a different property and rotate at intervals.

MATERIALS REQUIRED:

Per group:

• Results table [PDF version] [Word version]
• Security Department Fax [PDF version] [Word version]
• Testing kit (2 x AA batteries, battery holder with wires, a 3 V buzzer or bulb in a holder, crocodile clips/wires, magnet)
• Samples pack - all equally sized (e.g. 5 mm x 5 mm x 120 mm) (wood, polythene, perspex, brass, copper, steel, aluminium)
• Bicycle light
• Old floppy disc
• Small battery operated hand-held fan

Per class:

• Heat conductivity test station: plastic beaker half-filled with hot water, butter, tissue
• Density/mass test station: wooden seesaw, large samples of the materials listed above (e.g. 100 mm x 150 mm x 20 mm)

METHOD:

• In their groups, allow the children to investigate the properties of materials provided in order to complete the results table (details of the tests below)
• When finished introduce the crime which has been committed giving each group a copy of the fax from the Security Department
• Allow the children to investigate what materials each of the items are made of by taking them apart
• Ask each group to deduce who the main suspect is

Hardness:

1. Systematically scratch one sample with another to deduce an order for the hardest material through to the softest material.

Density:

2. Using the larger samples and the see-saw deduce the order in which the materials increase in weight.

Heat Conductivity:

3. Add a small knob of butter to the end of each of the samples. Each child in the group should hold 1-2 of the samples. Have the beaker of hot water at the ready and then stand all the samples in the beaker, butter up, at the same time. Watch to see which of the materials conducts the heat the quickest and melts the butter first.

Electrical Conductivity:

4. Construct a simple circuit to test the components. Following on from this test each of the samples to see if they conduct electricity.

Magnetism:

5. Test each material for its magnetic properties by placing the magnet near each sample.

THEORY:

• Hardness: Metals are harder due to their structure. The atoms are very close together in a tightly packed arrangement. The forces between the atoms are strong so that the atoms can stay close together. This makes the metals hard materials. The different strength forces keep the atoms together and so some metals are harder than others. Plastics and wood are softer as the forces between these atoms are weak and so it is easy to scratch these.
• Density: The close packing of atoms in metals mean that there are more atoms in the same volume when compared to the plastics and wood. Different types of atoms are different sizes and masses and so the density (the mass per volume) will vary between different metals.
• Heat Conductivity: Metals conduct heat well due to their structure too. The heat from the water makes the atoms vibrate more in the end of the sample dipped in the water. The atoms bang into their close neighbours and some energy is transferred making the neighbours vibrate more and so this carries on along the sample. The metals do not all conduct heat the same as the atoms are different in each metal and their arrangement varies very slightly. The plastics and wood do not conduct very well at all as their atoms are further apart, so the energy can not be transferred between them.
• Electrical Conductivity: In order for electricity to be conducted through materials there must be electrons available to carry the charge. In metals there are many electrons available for this purpose, unlike plastics and wood. Some metals have more electrons than others and so are able to conduct more electricity than other.
• Magnetism: In the case of this experiment, only steel is attracted to a magnet. This is because steel is comes from processed iron. Iron is a well known naturally occurring metal that is attracted to a magnet. Magnetism is related to special properties of the atoms known as the electronic structure.
• Materials Detectives results sheets [PDF version] [Word version].
  There will be some variation in the ranking of the metals for the hardest material and the best conductor of heat. The polythene, perspex and wood conduct heat poorly and any melting of the butter is probably due to any steam rising from the hot water.
• The exercise enables the children to choose fair tests to distinguish between the different properties of the materials investigated improving their scientific thought processes
• Solution to the crime [PDF version] [Word version].

WEB LINKS:

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