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Grade 6 (age 11-12)

grade 6 Energy Conversion

Energy is never lost or newly made; it changes from one form into another. In a light bulb, electrical energy becomes light and heat; in a car, chemical energy in the fuel becomes the kinetic energy of motion; in a plant's leaf, light energy becomes chemical energy stored in food. While a ball dropped from high up is falling, its potential energy goes down by exactly as much as its kinetic energy goes up, so the total of the two stays the same. Pick a device to see which energy turns into which, then change the ball's height to see the two bars hand energy back and forth.

Energy changes form

⚡ What is energy conversion?
①Energy changes from one form into another.
②Light bulb: electrical energy → light energy and heat energy
③Car: chemical energy in fuel → kinetic energy and heat energy
④Plant: light energy → chemical energy stored in food
⑤Along the way, some energy spreads out as heat that is hard to use, which is why saving energy matters.

Different kinds of energy

Kinds of energy
Kinetic / potential / heat / light / electrical / chemical / sound energy
Energy exists in many forms, and they can change into one another.
💡 Forms of energy
①Kinetic energy: the energy of a moving object; the faster, the more.
②Potential energy: the energy of an object up high; the higher, the more.
③Heat energy: energy that warms things.
④Electrical energy: energy that runs electrical devices.
⑤Chemical energy: energy stored in food, fuel and batteries.
⑥There is also light energy and sound energy.

Conservation of energy

80%
🔄 Conservation of energy
①Energy is never lost; it only changes form.
②When the ball is high up, its potential energy is large and its kinetic energy small.
③As it falls lower, its potential energy shrinks and its kinetic energy grows.
④The sum of the two stays the same as at the start. This is called conservation of energy.
⑤In real life some energy turns into heat as the ball rubs against the air, but adding that in, the total is still the same.

Summary

Conservation of energy
Energy only changes form; it is never created or destroyed
This is the law of conservation of energy.
Examples of energy conversion
Electrical → light (bulb) / Chemical → kinetic (car) / Light → chemical (photosynthesis) / Potential → kinetic (roller coaster)
Energy conversions happen all around us.
🎯 Key points
①Energy comes in many forms: kinetic, potential, heat, light, electrical, chemical and sound.
②Energy changes from one form into another.
③Conservation of energy: however it changes, the total amount stays the same.
④A falling ball turns potential energy into kinetic energy.
⑤Some energy becomes hard-to-use heat along the way, so saving energy matters.

Examples and Unit Test

Example 1
When a light bulb turns on, what is the main energy conversion?
1
A bulb gives off light when current flows through it.
2
So electrical energy becomes light energy, and some of it becomes heat energy too.
▸ Electrical energy → light energy (and heat energy)
An old-style bulb gets hot after a while because part of the electrical energy has turned into heat.
Example 2
A ball is let go from a high place. While it falls, how do its potential energy, its kinetic energy and the sum of the two change?
1
Its height drops, so potential energy goes down; it speeds up, so kinetic energy goes up.
2
Potential energy is turning into kinetic energy, so the sum of the two stays the same.
▸ Potential energy goes down, kinetic energy goes up, and their sum stays the same.
In the second picture, as you lower the height, the red bar grows by exactly as much as the blue bar shrinks.
Unit-test style
Which statement about energy conversion and conservation is correct?
①Energy disappears completely once it is used.
②A light bulb turns electrical energy into light energy.
③A falling ball's kinetic energy gets smaller and smaller.
④A car turns kinetic energy into chemical energy.
⑤Photosynthesis turns chemical energy into light energy.
▸ ② A light bulb turns electrical energy into light energy.
1
A light bulb is a classic example of turning electrical energy into light (and heat) energy.
2
Energy only changes form and is never lost (①), a falling ball's kinetic energy grows (③), a car turns chemical energy into kinetic energy (④), and photosynthesis turns light energy into chemical energy (⑤).
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