الأسبوع 17 · المحور الثالث، الوحدة الثالثة، المفهوم 3.1 «الأجهزة والطاقة» (ب): سلاسل الطاقة وحفظ الطاقة · 3 دروس
1
Energy chains that start at the Sun
Discovery Education Science P4: Term 2, Unit 3, pp. 11–25
GoalTrace the energy of a device back to its source and draw an energy chain that starts at the Sun.
New words
energy chain · a diagram that shows the path of energy from its source to a devicetransform · to change energy from one form into anotherpower plant · a place where fuel is used to make electricity
Explanation
Almost all the energy we use started as sunlight. To prove it, we draw an energy chain, which shows each link on the path of energy. Eating is a simple chain: sunlight shines on an orange tree, the leaves change the light into chemical energy stored in the fruit, you eat the fruit, and your body uses the chemical energy to move. Heating a pan of water over a wood fire is another chain: sunlight, the tree stores chemical energy, burning wood releases thermal energy, and the water gets hot. A hair dryer is harder. Its electrical energy came along a cable from a power plant, where coal or natural gas was burned. Coal and gas are made from ancient living things, and those plants once got their energy from the Sun. So the chain begins at the Sun.
Sun: light→tree: chemical→fire: thermal→water gets hot
Worked examples
Sun→banana plant→Seif’s body→kick
Seif eats a banana before football. Chain: Sun (light) to banana plant (chemical energy stored in the fruit) to Seif’s body (chemical energy used) to a kick (motion).
A solar water heater on a roof in Aswan: sunlight (light energy) heats the water in the panel (thermal energy). It is a short chain with only two links.
Sun→ancient plants→coal or gas→power plant→hair dryer
Hair dryer chain: Sun (light) to ancient plants (chemical) to coal or gas (chemical) to power plant (thermal, then motion, then electrical) to hair dryer (electrical to heat, motion and sound).
Class activity
Chain cards. Draw or cut out pictures of the links of an energy chain on paper cards: Sun, plant, food, you running. Mix the cards and put them in the right order, with arrows between them. Then make a chain for a lamp at home. Do not touch sockets. Label each link with the form of energy.
Practice
1
Put the links in order. A: you run. B: sunlight. C: a plant makes food. D: you eat the food. Say the letters.
B, C, D, A.
2
Where did the energy in coal come from, long ago?
From the Sun: the ancient plants that became coal used sunlight.
3
Finish the chain: wood fire to heat to a pan of water. What form of energy does the burning wood release?
