Changes in the Field (30 min)
When we did this activity we used our own photographs, which are not yet on this site, but we have since found an equivalent on the education wing of the National Farmers Union website, known as 'field-to-fridge' - check-out http://www.ukagriculture.com/field_to_fridge_face/fieldtofirdge_face_htm to go straight there and follow the growth of a number of different crops. Challenge the children to arrange the 'farming year pictures' in chronological order, adding captions to the pictures describing the changes that are happening to the plants and the land.
Melting Chocolate (25 min).
Make foil “baskets” large enough to support a piece of cooking chocolate or chocolate button held over a nite-light. Nite-light holders are available and recommended. Describe the solid chocolate, observe carefully the melting process (caused by heating), describe the liquid chocolate, allow to cool and describe the solid formed upon cooling – CARE foil baskets will be hot. They can be placed on ice to speed cooling.
Waterlogging (25 min). Two different experiments here …
(i) Imitating what may happen in the field and designing a fair-test. The children should prepare a small plant pot (strips as used in garden centres are ideal as they use less soil & take up less space) - put soil in the pots and sow seeds – make predictions about what will happen, any seeds should do, again wheat is our staple. Water regularly but stand the ‘waterlogged set’ in water at all times and place all the pots in a warm, sunny position. Grow for about a month and see if there are any differences – seeds may rot and thus fail to germinate, otherwise the waterlogged plants may grow shorter/taller, be yellow in colour or have a damaged root system.
(ii) Soak mung-beans overnight in water and then divide into 2 sets – treat one set as in Lesson 2 (germination), using wet filter papers, but keep the waterlogged set totally covered with water and therefore deprived of oxygen – links to “lights-out” – see below.
Natures Anti-Freeze (20 min)
Advance Preparation: Make a collection of leaves, a mixture of rhodedendron leaves (or any evergreen bush) and lettuce leaves is ideal. Place in a bag and freeze (preferably overnight).
Take the frozen leaves out of the freezer, observe, allow to thaw and examine again. Annuals, such as lettuce, will have become soft and mushy while the evergreen will have kept their shape.
How cold is ice? – with an ICT-link (40 min)
Begin with predictions about the temperature of ice. A number line may help here.
Give each child a small tube/container of crushed ice. Measure its temperature using a thermometer – ensure thermometer is used correctly. Record class temperatures on a spreadsheet and calculate an average. Note amount of variation between readings. Small.
Defrost the ice to make a solution of cold water and as soon as the ice has melted – requires careful observation and challenge the children to think how they are making the ice melt, an input of energy – remeasure the temperature. Record class values on the same spreadsheet and calculate an average again. The values given will be much more variable. Why? The volume of liquid will vary, particularly if you give out variable amounts of ice in the first instance. Larger volumes will take longer to heat-up and will therefore have lower temperatures. A good way to demonstrate the importance of repeat readings.
Lights-Out (20 min)
Ignite a single nite-light. Cover with one of 3 or 4 differently-sized glass mixing bowls from the kitchen. Time how long it takes for the flame to be extinguished. Make repeat readings, vary the number of nite lights?? It all comes down to oxygen deprivation again, as per the waterlogging experiment. Extension activity – find out the volume of air each nite-light is burning within, by adding water to the bowl and measure how much water.
Demo; Freeze-thaw in ‘rocks’ (Links to Lessons 1 & 3)
Find a small, thin-walled glass bottle. Fill completely with iced water ensuring there are no air-bubbles. Screw the top on tightly and place it in the middle of a medium-sized beaker. Surround the sealed bottle with a ‘freezing mixture’ of crushed ice and salt: start with a centimetre depth of ice, then a liberal amount of salt, and repeat until bottle is completely covered. Final proportions should be approx. 3 ice: 1 salt. Observe fall in temp – it occurs quickly and is quite dramatic – a data-logger would be ideal but we used a standard thermometer. The temp will drop to approx –20oC. If the glass bottle is sufficiently thin, then shattering will occur quickly (5-10 min) even before its contents are completely frozen, by cracking at the base due to a build up of pressure. Including food colouring in the bottle may help visualise when this has occurred. (Ref: Heselden, SSR 84:121-122).