Science at key stage 3    (Year 8)

• Use two introductory activities to help pupils recall previous measuring experience and to raise the issue of scales.
• Two pupils put their hands in water, one in cold and the other in warm, then both simultaneously put their hands in lukewarm water and report how it feels; one claims it's warm, the other that it's cold. Ask them to check the temperature with a thermometer.
• Ask pupils to suggest values for common temperatures, eg freezing water, boiling water, room temperature, outside temperatures during different seasons, body temperature, the coldest place on Earth, the hottest place on Earth, hot oven temperature, safe (hygienic) fridge and freezer temperature. Then pupils:
• measure or otherwise find out about these temperatures and produce a chart of temperatures such as a 'temperature line' or bar chart; or
• conduct a survey of perception of temperature values with adults or other class groups, and work out how much those surveyed estimate values too high or too low

• Demonstrate or arrange for groups to use different thermometers to measure a range of temperatures.

• Remind pupils of year 7 work on the heating effect of burning fuels, where energy was released to cause temperature rise. Discuss the energy flow associated with the cooling of boiling water and the warming of ice in the classroom.
• Elicit pupils' ideas about how heat and temperature are linked and establish that they are not the same thing. Ask pupils to predict and observe how the temperatures change when they, eg mix volumes of hot and cold water, boil different quantities of water with the same heater.
• Through questioning, help pupils explain why their predictions matched or did not match the observations they made.

• Ask pupils to touch a number of materials, eg wool, metal, polystyrene, rubber, wood, glass, etc, and decide which feels coldest/warmest. Summarise opinions. Point out that all materials are at the same temperature - room temperature. Explain that the sensation of coldness is caused by the best conductors of heat conducting their body heat away most quickly. The temperature difference causing this flow of energy is between the pupils themselves and the object they touched. Remind pupils that we have a near-constant body temperature of about 37?C. Ask how this compares with the objects touched.

• Ask pupils to work in pairs to suggest why certain materials are used in cooking utensils, eg a wooden spoon (or saucepan handle) and a metal saucepan base. Demonstrate the difference in rate of conduction of heat, eg using temperature probes and dataloggers to determine temperature of the tip of a rod and monitor the rate of temperature rise; temperature probes along length of rod. Use the demonstration to classify materials as good or poor thermal conductors.

• Demonstrate poor conductivity of water by trapping an ice cube at the bottom of a tube of boiling water using a small piece of gauze. Heat the top of the water to boiling point and show that the ice remains unmelted at the bottom. Temperature sensors linked to a computer could monitor different positions in the tube.
• Show highly effective insulating materials, eg expanded polystyrene, filling for duvets, and demonstrate that they are mostly trapped air, eg evacuate a sample with a vacuum pump.

• Recall with pupils the idea that solids are made of particles called atoms and molecules. Introduce the idea that when energy as heat is absorbed by a solid, the particles move around their position in the solid more. This movement can be passed on to adjacent particles. Get pupils to enact this model of conduction: ask them to link arms firmly in a line (simulates a solid), then one pupil provides energy ('heats the line') by gently pushing and pulling the end of the line. The energy (movement) is conducted along the line. This happens less well if they are merely holding hands (liquid) and not at all if they are not linked (gas).

• Remind pupils of the different ways in which particles are arranged in solids, liquids and gases.
• Carry out a quick demonstration of expansion of a solid on heating, eg 'ball and ring', or by heating a horizontal metal rod clamped at one end, with the other end free to roll over a pin with a small paper flag attached. Discuss with pupils and get them to model, in terms of particles, why the rod/solid expands and contracts. Ask them to use the particle model to predict what would happen if a liquid or gas were heated or cooled, and check the prediction by demonstration or pupil practical work, eg
• warm in a water bath a boiling tube filled with oil, with a bung placed in the top, into which has been placed a narrow vertical glass tube with the oil level part way up
• warm with hands a large round flask containing water with a bung in the top, into which a narrow vertical glass tube has been inserted; either insert a small bead of oil in the glass tube, or invert the open tube into the water and watch the air bubble out
• Ask pupils to use the observations to explain why it would be dangerous to heat a completely sealed container of a liquid or gas.

• Review pupils' ideas of upthrust and density by showing a helium balloon rise or by using similar stimulus material.
• Build a (tethered) hot-air balloon using 'night lights' as the source of hot air, or build a windmill suspended from a thread to be driven by the hot air rising from a 100W light bulb. Establish that these work because heated air moves upwards since it is less dense than cooler air, and point out that the air will come down as it cools.
• Use forceps to drop a crystal of potassium manganate (VII) down a glass tube into water, which is then warmed over a Bunsen burner, and observe the trail of purple water formed due to the convection current. Alternatively, place a bottle containing cold, colourless water on top of a bottle containing hot coloured water, so that the contents can mix. Repeat with the bottle containing the cold colourless water on the bottom.

• Offer pupils a mixed-up written explanation of what they have just seen, including reference to energy transfer, and ask them to sequence it chronologically to describe convection currents.

• Remind pupils that in a solid the particles are closely packed, while in fluids they can move past each other. Encourage them to speculate how the absorption of heat by fluids will cause movement of these particles.
• Present a model in which some pupils acquire energy, eg coloured paper resembling banknotes, from the source at the front of the room. Explain that those with the most money move fastest, but when they meet the others they give money away. So pupils move from the source towards the back of the classroom (top of the container) distributing money/energy on the way. Others take their place to be provided with energy until they are all warm.

• Remind pupils that in a solid the particles are closely packed, while in fluids they can move past each other. Encourage them to speculate how the absorption of heat by fluids will cause movement of these particles.
• Present a model in which some pupils acquire energy, eg coloured paper resembling banknotes, from the source at the front of the room. Explain that those with the most money move fastest, but when they meet the others they give money away. So pupils move from the source towards the back of the classroom (top of the container) distributing money/energy on the way. Others take their place to be provided with energy until they are all warm.

• Conduction and convection both need particles to carry energy when heat is transferred. Ask pupils if heat can travel through nothing at all (a vacuum).
• Draw connections between the behaviour of heat and light from the Sun, eg both radiate from the source. Demonstrate focusing (use of burning glass) and reflection of infrared radiation using radiant heaters or hot light bulbs.

• Review pupils' key stage 2 work on insulators, where they may have investigated keeping cups of liquid warm or preventing ice cubes melting.
• Recap year 7 work on the need to conserve energy resources. Ask groups to discuss the ways used to prevent energy escaping from homes, eg loft insulation, heavy curtains, cavity-wall insulation.
• Use models to explain how these methods work, eg double glazing, draught excluders.

• Ask pupils to devise a way to compare the effectiveness of different insulation techniques, using a small lamp as a heating source in an 'energy house', eg use dataloggers to produce on-screen graphs of heating or cooling. Help pupils to decide what factors to consider, eg the starting temperature of the house and thickness, nature and positioning of insulation material.
• Encourage pupils to make some trial measurements and to consider how to present their data and draw conclusions. Ask pupils to evaluate their work and draw inferences for use in everyday contexts.

• Provide pupils with information sources so that they can discuss the pros and cons of different ways of insulating a typical home, eg using manufacturers' claims for double glazing. They should attempt to explain their ideas using particle explanations and the concept of heat transfer through materials.

• Ask pupils to use the particle model to predict what might happen if heating of a solid or a liquid eg wax, water, continued indefinitely.
• Use ICT simulations to illustrate the particle model explanation for melting, boiling, freezing/solidifying.
• Invite pupils in groups to measure and record every half minute the temperature of one (or more) material as it changes state, eg
• ice as it melts
• water as it boils
• salol (phenyl salicylate) as it melts
• salol (phenyl salicylate) as it freezes
• Ask pupils to plot their data on a graph and show them how to draw an appropriate curve, or use temperature probes with a datalogger, to produce a real-time graphic display. Ask pupils to describe or tell the story of what happens to the temperature. Establish through discussion of their data and some data from secondary sources that changes of state occur at a fixed temperature. Challenge pupils to tell the story of what would happen if their particular substance were cooled or heated again.

• Bring together pupils' ideas developed in this unit by:
• asking them to produce a leaflet which gives an example and an explanation of heat transfer in a situation of interest to them, eg on a mountaineering expedition above the snowline; on a beach holiday; cooking on a barbecue. Encourage imagination and ask for explanation. The audience for their leaflet may be parents, younger pupils, the general public
• providing a large picture of a seaside scene including sea, sand, Sun, sunbather, beach barbecue, parasol, swimmer, balloonist and onshore wind. Ask pupils to identify all the situations of energy transfer and which mechanism is responsible, and to label and explain each item briefly