What is heat energy?
Heat is a form of energy that makes things warm or hot. It is produced by many things and even though it cannot be seen, we can feel its effects with our sence of touch (i.e. things feel hot).
Heat also flows from things with a higher temperature to things with a lower temperature. Many kids confuse heat and temperature but they are not the same thing.
What is temperature?
Temperature is a measure of how hot a thing is. Something that is hotter will have a higher temperature. You can measure temperature with a thermometer.
More about the measurement of temperature:
The unit of temperature is degrees Celsius (written °C) or degrees Fahrenheit (written °F). For example, the temperature of ice is 0°C or 32°F. Although they are referring to the same temperature, the numbers used are different when the unit is different. You can also convert temperatures between °C and °F.
Did you know? The normal human body temperature is about 98.6°F or 37°C
Sources of heat for kids
Anything that produces heat is known as a source of heat. Our planet's primary source of heat is the sun. It is the most important source and without the sun, it would be too cold for most living things on Earth to survive.
Besides the sun, other examples of heat energy sources are:
- Nuclear power stations, which produce large amounts of heat through nuclear fission
- Household appliances such as stoves, electric irons, toasters, and ovens
- Burning of fuels such as wood, oil, coal, and natural gas
How does heat flow?
We all know that the temperature of objects do not remain the same all the time. For example, if you leave a cup of hot chocolate on the table for a while, the hot chocolate will soon cool down to room temperature. This happens because heat flows from objects of higher temperatures to objects of lower temperatures. In the case of the hot chocolate, heat flows from the cup of hot chocolate to its surroundings (the table, the surrounding air, etc). Once the hot chocolate is the same temperature as the surroundings, heat stops flowing away from it.
Heat gain and heat loss
When an object becomes colder, we say that it has lost heat. Conversely, when an object beomes hotter, we say that it has gained heat.
Using our hot chocolate example again, we can say that the hot chocolate has lost heat to its surroundings. Similarly, if you place a cold drink in a room, the cold drink will gain heat from its surroundings until it becomes the same temperature as the rest of the room.
More examples of heat gain and heat loss:
- Holding an ice cube in your hand - The ice cube gains heat from your hand and your hand loses heat to the ice cube
- Putting an ice cube in a warm drink - The ice cube gains heat from the warm drink and the warm drink loses heat to the ice cube
- Boiling water over a fire - The water gains heat from the fire
Effects of heat gain and loss
When objects gain or lose heat, they not only become hotter or colder, they can also expand, contract, or change their state.
Expansion and contraction
- Objects become bigger when they gain heat. They expand.
- Objects become smaller when they lose heat. They contract.
Practical uses for expansion and contraction:
- Non-digital thermometers contain either alcohol or mercury that expand and contract when they gain and lose heat respectively. When used on a warmer object, the alcohol or mercury in the thermometer expands and the reading moves up, showing a higher temperature. On the other hand, when used on a colder object, the alcohol or mercury contracts and the reading goes down (becomes smaller), showing a lower temperature.
- When baking bread, the gas inside the bread expands and causes the bread to rise.
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Changes in State
Heat gain and heat loss can cause a change in state in matter. Water is the best example for changes in state.
- Solids can turn into liquids - Ice melts into water above 0°C
- Liquids can turn into gases - Water evaporates into water vapor or boils into steam (at 100°C)
When objects lose heat
- Gases can turn into liquids - Water vapor or steam condenses into water droplets
- Liquids can turn into solids - Water freezes into ice at 0°C
Heat conduction for kids
A conductor of heat is something that allows heat to flow through it. Objects can be classified into good or bad conductors. Bad conductors of heat are also known as heat insulators.
A good conductor allows heat to flow through it easily. This also means that they gain and lose heat faster. Examples of good conductors of heats are metals such as steel, iron, aluminium, and so on. Because they are good conductors of heat, we usually use these metals for cooking. This makes food cook faster as heat is passed to the raw food more quickly, turning it into cooked food.
A bad conductor or insulator of heat does not allow heat to flow through it easily. This also means that they gain or lose heat slower. Examples of poor conductors of heat are plastic, wool, rubber, wood, and air. We can use insulators of heat to keep things warm. For example, woolen jackets help us keep warm because they do not conduct heat away easily.
You've learnt the concepts now try some experiments
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