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Energy & Forces - Conversion & transfer of energy - Energy sources - G19
This is the Teacher's Guide for this targetThis is the Teacher's Guide for this targetTeacher's Guide


1. This parallels some of the work on power production in P6 Group 17 - ES-D3.3 and P7 Group 23 - EF-D2.1.

Start this unit with a class discussion about the fuels they use at home. For most children gas, barbecue charcoal and electricity (not actually a fuel but a form of energy) will be the only fuels they come across.

Coal was formed from plants and animals which died when the Earth was covered with swamps.

About 300 million years ago these swamps were home to giant plants and many animal species lived there. Over millions of years the plants and animals lived and died and got buried under the mud at the bottom of the swamp. The mud gradually hardened into rock and the layers of rotting plant and animal material were squashed between heavy layers of rock and heated by the Earth. Over millions of years they changed into coal. Coal seams are also associated with pockets of gas which can make them very dangerous to mine. Coal can be very deep under the ground in which case huge tunnels are bored and the coal mined out or it may lie just under the surface and can be mined using open-cast methods.

2. Oil, coal and gas are fossil fuels - so-called because they were formed from the remains of prehistoric plants and animals.

Oil and Gas were formed over millions of years and come from the remains of tiny animals that lived in the seas in prehistoric times. As the animals rotted they were covered by more and more layers of animals and finally by mud and sand. The rotting animal matter gradually turned into oil and also produced methane much the same as our rubbish tips do now. The gas was trapped under the successive layers of silt and mud on top of the oil layer and formed huge pockets containing many millions of litres.

Oil is reached by drilling holes in the ground which may have to go down thousands of metres. Once the oil is reached, it may gush out under pressure or may have to be pumped out and up to the surface.

Nearly half the world’s oil is found under the sea floor which can add even more length to the drilling operation. Huge oil rigs are towed out from the shore and anchored in place over the drilling site. Once the supply is tapped they send oil ashore through sea-bed pipelines or use tankers to ship it to the refineries, where it is split into many useful components - petrol, aviation fuel, oil for heating, diesel, petrochemical products for the chemical and plastics industries etc.

Gas is also tapped using rigs and is piped back to huge storage tanks on land.

As a further activity, Worksheet D10 (G) from the P6 units could be revisited.

3. Try to collect nutritional panels from a wide variety of foods - perhaps this could be done over a period of a week or two before starting this topic. Look at the labels and compare the ‘Energy’ values for different foods.

Scientists measure all energy in a unit called the Joule. This is the metric unit of energy and if you look at the nutritional panel you will see that nowadays, energy values are given in kJ and in kcal.

Point out to the children that the energy value of food is always given as ‘How many kJ in 100 ml or 100 g’ In some cases it will also be given as ‘How many kJ in one pot/ bar/ biscuit etc’. By comparing how much in 100 ml or 100 gm we get a fair comparison. It is not easy to judge whether a pot of yoghourt with 98 kJ is a higher energy food than a biscuit with 78 kJ since they are different sizes and weights. To be fair, we need to compare the same amounts of each type of food and the per 100 g or per 100 ml value allows us to do this.

A data handling exercise could be done by sorting the panels into different food groups - dairy products, meat, vegetables, sweets etc. Compare the energy values of foods within each group and then compare the groups. Remember that this exercise is primarily about energy and not about the fat and vitamin contents etc.

The children could use the labels to piece together a diet for the day, different groups could be set different targets If possible find out what different athletes have as their daily targets - how many kJ do weight lifters eat? How many do marathon runners eat? The children may be able to find out these numbers depending on their interests.

Who can find the food with the highest energy value?

An alternative would be to let the children make a chart of the energy values of their ten favourite foods.

Worksheet D19 (G) can be used for this activity.

Joule purpose

Most people know the unit ‘Calorie’ as a measure of how much energy is in food. This is a rather confused use of the term since a calorie is a tiny unit and the number of Calories listed on food packets are kilocalories - thousands of calories. People counting calories for a diet are actually counting thousands of calories and their intake will be in the region of 1500 kilocalories per day although we always just say 1500 Calories.

Yogurt cartons etc which say ‘only 98 Calories per pot’ on the front will have 98 kcal written on the nutritional panel at the back.

In science, we no longer use the calorie as a unit of energy. The joule is used instead.

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