Science at key stage 3    (Year 8)

• Show pupils samples of rocks and ask them to sort them into groups. Ask them to explain the basis for their groups, prompting if necessary by asking questions, eg What makes the rock shiny? What can you see in the rock? Is the rock all the same colour? Ask pupils to record key responses. Discuss with them the words/observations that occurred most frequently.
• Provide pupils with samples of granite and sandstone and ask them to explore their textures, eg by close observation using a magnifier and by immersion in water. Ask pupils to explain why one rock produces bubbles in water and the other does not. Investigate the absorption of water by weighing samples before and after immersion to illustrate porosity. Model interlocking and non-interlocking textures, eg using a three-dimensional block puzzle and marbles, and relate observations to interlocking and non-interlocking textures. Ask pupils to record and explain their findings using annotated drawings and diagrams. Establish the idea that rocks are almost always mixtures of materials.

• Take pupils to observe rock materials out of doors, eg in a cemetery or on a high street, or show them pictures, video clips of rocks/building materials in the locality of the school.
• Ask pupils to compare older surfaces with new or chipped surfaces to record evidence of discoloration and/or crumbling. Ask them to speculate about possible causes. Note the effects of weathering under trees or adjacent to soil and ask pupils to suggest reasons for this.
• Remind pupils about earlier work on acids and alkalis and show that samples of rainwater are slightly acidic.
• Ask pupils to compare fresh granite with weathered granite to observe any changes to minerals. Simulate wet, oxygen-rich, acidic conditions using dilute hydrochloric acid and hydrogen peroxide in a 50:50 mixture. Place a sample of granite in the solution and capture the changes daily for up to two weeks using a digital camera to create a time-lapse sequence. Ask pupils to examine, describe and explain the changes using a computer-generated slide show. Discuss with them why this is an effective way of recording results.

• Show pupils pictures or a video clip as a stimulus and ask them to suggest why mountaineers climbing in high mountains, eg the Alps or Himalayas, start early in the morning and try to complete their climbing on mountain faces before midday.
• Demonstrate the magnitude of the forces arising from expansion or contraction of a solid, eg by repeatedly heating a corner of a chip of granite to red heat then quenching it in cold water or by using a breaking-bar experiment. Establish with pupils that these forces are large enough to cause pieces of rock to break off and are most significant where there are large temperature ranges.
• Present pupils with a rock sample containing cracks and soak in water. Explain that this is to be used to model what happens when water freezes and thaws. Ask them to suggest how this might be done and how to record the results. Use a digital camera to create a time-lapse sequence showing the number of freeze-thaw cycles on the rock sample and ask pupils to examine the changes, particularly the width of cracks and the shape and size of fragments, using a computer-generated slide show. Discuss how the angular fragments are formed. Ask pupils to re-evaluate their suggestions about mountaineers and explain why rockfalls can be a major hazard to climbing.

• Show pupils photographs of natural scree slopes, eg Wast Water in the Lake District, and ask them to suggest how rock ended up as fragments in a pile at the bottom of the cliff and what the scree slope tells us about past conditions. Ask pupils what characteristics would lead to rocks being weathered easily.

• Review work on weathering and fragmentation of rocks. Find out pupils' ideas about how rock fragments are transported and changed by asking them to sequence a set of statements/drawings and to explain their sequence. Help pupils to investigate water flow in a channel and its overflow by using square guttering that channels water into a large trough. Use a dye, eg ink, to track what happens to the current along the gutter and in the trough. Discuss the spreading out of the dye and ask pupils to describe and record where water is moving quickly, and where it is moving slowly, and to use the results to predict where large and small fragments will be deposited.

• Ask pupils to suggest how water flow might affect the movement of different-sized grains of sediment and to plan how to investigate a specific question using gravel, sand and muddy soil. As part of their investigation, ask pupils to observe and record the distribution of sediment grain size along the gutter and to explain the relationship with volume and speed of water flowing. Bring together the outcomes of all investigations, asking pupils to describe what they did, what problems they encountered and how they overcame them.

• Show pupils that the change in sediment shape and size during transportation can be simulated by shaking plaster cubes in a cylindrical container. Ask them to investigate what happens over several cycles of tumbling in terms of, eg number, average, mass or shape of fragments after each cycle. Ask pupils to show the results as line graphs or appropriate drawings, and to explain what has caused the changes and what happens to the 'lost' mass. Bring together the class results with the pupils, and help them to make generalisations about fragmentation.

• Show pupils photographs, video clips of rivers full after a storm and in normal state and ask them a series of questions, eg
• Why does the river appear dirty?
• Where has the dirt come from?
• What happens when the water level drops?
• Why does the river become clearer?
• Help pupils to generate key points about transportation and formation of sediment grains from their responses and the responses of others.

• Show pupils photographs or video clips of cliffs with sedimentary strata and ask them to suggest, eg in drawings or annotated diagrams, how the layers were formed.
• Ask pupils to investigate how quickly sediment settles using grains of different sizes, eg clay, sand, gravel, in a jar of water.
• Ask pupils to observe if the layers have sharp boundaries or grade into each other and to relate this to the conditions under which the layers were formed. Ask pupils to speculate about what controls the thickness of layers and to explain their ideas to others.

• Ask pupils whether water in rivers, lakes, seas has solids dissolved in it. Remind them of earlier work on different types of water. Ask them to explain the origin of the salts. Use a flow diagram to explain how salts become concentrated in seas or lakes. Ask pupils to suggest what would happen if the seawater evaporated and how to test their ideas. Modify the flow diagram to discuss how seas and lakes can dry up.
• Explore with pupils how a sequence of sediments can be built up by covering the residue from evaporated sea water with a layer of clay and shells to represent the remains of dead organisms, adding more seawater and allowing it to evaporate. Extend to the formation of oil, eg by using video clips.
• Give pupils a simplified diagram showing different strata and ask them to tell the story of how the layers were formed and why fossils are often found in sedimentary layers.
• Extend by asking pupils to use secondary sources to find out about Mary Anning and the fossil specimens she collected.

• Provide pupils with a series of photographs/diagrams/drawings and brief descriptions, eg a muddy river estuary - grains of mud and sand deposited at the edges of rivers; a pile of rocks at the bottom of a scree - water that gets into cracks and expands as it freezes, and ask them to match them. Where pupils have matched images and descriptions in different ways, ask them to justify their choices to each other.