Week 18 · Theme 3, Unit 3 Energy and Fuels, Concept 3.2 About Fuels (A) · 3 lessons
1
A road trip with no fuel
Discovery Education Science P4: Term 2, Unit 3, pp. 26–39
GoalExplain what a car does with petrol, calculate how far a tank can take it, and ask good questions about fuels.
New words
petrol · a liquid fuel made from oil that is burned in car enginesengine · a machine that burns fuel to make a vehicle movefuel gauge · a dial that shows how much fuel is left
Explanation
A family drives along a long desert road toward Alexandria. The fuel gauge is low and there is no petrol station for many kilometres. The car sputters and stops. Why? A car’s engine burns petrol. The chemical energy stored in the petrol is released as heat inside the engine, and the engine changes it into motion, with some heat and sound too. When the tank is empty, the car has no energy source left and cannot go on. We can work out how far a tank will take a car. If a car uses 8 litres of petrol for each 100 km, then 40 litres will take it 40 ÷ 8 = 5 lots of 100 km, which is 500 km. Could a car run on sunshine? Some small cars do, with solar cells and batteries, but they cannot drive at night without stored energy. Scientists ask: what are fuels, where do they come from, and what else can give a car energy?
petrol: chemical energy→engine burns it→motion, heat and sound
Worked examples
Distance
Petrol needed
100 km
8 L
200 km
16 L
300 km
24 L
A car uses 8 litres of petrol for every 100 km. The road trip from Cairo to Alexandria is about 200 km. It needs 2 × 8 = 16 litres. A full tank of 40 litres is more than enough.
Dad notices that the fuel gauge shows almost empty. He drives to the next petrol station and a worker fills the tank. Only workers handle the pump. Children keep away from petrol.
Hana asks: Could a car run on sunshine? Her teacher says some small solar cars exist, but a car also needs energy for night and cloudy days. Good questions lead to investigation.
Class activity
Fuel questions. Ask a grown-up where your family buys fuel and what for. Write five questions about fuels that you would like to answer, for example: What is petrol made from? Why does a car need an engine? Which questions can you investigate with a book or a video?
Practice
1
What does a car engine do with petrol?
It burns it to release energy that makes the car move (with some heat and sound).
2
A car uses 6 litres for each 100 km. How many litres does it need for 300 km?
3 × 6 = 18 litres.
3
A tank holds 30 litres and the car uses 5 litres per 100 km. How far can it go?
30 ÷ 5 = 6, so 6 × 100 = 600 km.
4
Why can’t a car that uses only solar cells drive all night?
There is no sunlight at night, so it needs energy stored in a battery.
