What Is Heat In Science Kids?

What is heat?

Heat is a form of energy that is transferred from one object or system to another due to a difference in temperature. Unlike temperature, which is a measure of how hot or cold an object is, heat is the flow of thermal energy driven by a temperature difference.

For example, when you touch a hot stove, heat flows from the stove into your hand because the stove is at a higher temperature. This transfer of thermal energy is what we call heat. As heat transfers into your hand, the thermal energy causes the molecules in your skin to move faster, increasing their temperature.

Some other examples of heat transfer include boiling water on a stove, an ice cube melting in a warm room, or a computer chip heating up as electricity flows through it. In all cases, heat is energy transferred due to a temperature difference.

How is heat measured?

Heat is measured using units called temperature scales. The most common temperature scales are Celsius, Fahrenheit, and Kelvin.

In the Celsius scale, water freezes at 0°C and boils at 100°C. Temperatures can be negative or positive in Celsius. In the Fahrenheit scale, water freezes at 32°F and boils at 212°F. The Fahrenheit scale is used more commonly in the United States.

Temperature is measured using thermometers. Some common types of thermometers are:

  • Liquid thermometers – These contain liquid which expands when heated. Common liquids used are mercury, alcohol, and colored water.
  • Digital thermometers – These use electronic sensors to measure temperature. Many have digital displays.
  • Infrared thermometers – These measure infrared energy emitted from an object to determine its temperature without contact.

Thermometers must be placed properly to get an accurate reading. Oral and rectal thermometers measure body temperature, while oven and refrigerator thermometers measure air temperature.

What causes heat?

There are three main causes of heat in science:

  • Friction between objects – When two objects rub against each other, the friction between them generates heat. For example, rubbing your hands together warms them up because of the friction.
  • Electrical current flows – Heat is produced when an electrical current passes through a conductor. The more current, the more heat is generated. This is why electrical wires get hot when a lot of current flows through them.
  • Chemical reactions – Chemical reactions, like combustion, oxidation, cell metabolism, etc. involve the breaking and formation of chemical bonds. This releases or absorbs energy, usually in the form of heat. For example, the chemical reaction of burning wood produces a fire’s heat.

So in summary, on a molecular level, heat originates from the kinetic energy of atoms and molecules in matter. The faster they move, the higher their kinetic energy, which we perceive as heat.

Heat Transfer Methods

There are three main ways that heat energy can be transferred from one object or system to another:


Conduction is the transfer of heat between objects that are in direct contact with each other. The better the conductor, the more rapidly heat will be transferred. For example, a metal spoon left in a hot cup of soup will quickly gain heat from the soup through conduction.


Convection is the transfer of heat by the movement of heated particles from one place to another. For example, when water is heated on the stove, the warmed water rises while the cooler water sinks – this circulation of moving hot and cold material is convection.


Radiation is the transfer of heat in the form of electromagnetic waves or photons. The heat and light from the sun reaches us across space mainly by radiation. No direct contact is needed for heat transfer by radiation.

Effects of Heat

Heat can have dramatic effects on matter by increasing the energy of atoms and molecules. Some of the most notable effects include:

Melting Solids

When a solid absorbs heat energy, the atoms and molecules gain energy and vibrate more. If enough energy is added, the orderly structure of the solid breaks down and the solid melts into a liquid. This is why heating ice cubes causes them to melt into water.

Evaporation of Liquids

With more heat energy, liquid molecules move faster and faster until they transition from a liquid to a gas and evaporate. This is why heating water causes it to boil and evaporate into steam.

Expansion of Matter

As heat increases the vibrational motion of atoms and molecules, matter takes up more space. This causes most materials to expand when heated. One example is hot air rising since it becomes less dense than surrounding cooler air.

Heat in everyday life

Heat plays an important role in our everyday lives. Here are some of the main ways we experience and use heat on a regular basis:

Cooking food

One of the most common ways we use heat is to cook our food. Applying heat through methods like baking, boiling, frying, etc. transforms raw ingredients into delicious meals by changing their chemical structure.

Heating homes

During colder months, we rely on heat to warm our living spaces. Central heating systems and standalone heaters convert electricity or burn fuels into heat energy that keeps indoor temperatures comfortable.

Hot things can burn

Heat can be dangerous at high temperatures. Touching hot stovetops, irons, or anything significantly above body temperature can cause painful burns. Young children need to be especially careful around hot objects.

Staying warm in winter

Bundling up in warm clothes helps us retain body heat in cold weather. Hats, coats, gloves, and other winter wear provide insulation to maintain a comfortable temperature and prevent frostbite.

a child bundled up in a winter hat, coat, and mittens.

Heat Safety

It’s important for kids to practice heat safety to avoid getting burned or having skin damage. Here are some tips:

Avoid Getting Burned

Be careful around hot objects like stoves, irons, or anything that could burn you. Only touch things once an adult says they are cool enough. Stay away from open flames like candles, grills, or campfires.

Fire Safety

Fires can start quickly and spread fast. If there is a fire, leave the area right away and tell an adult. Never play with matches, lighters, or flames. Make sure you have working smoke detectors in your home.

Protecting Skin/Eyes from Sun

The sun’s light and heat can damage skin and eyes. Wear sunscreen when going outside and reapply often. Wear hats, sunglasses, and protective clothing. Don’t look directly at the sun.

Heat energy applications

Heat energy has many important applications in our modern world. Some of the main ways we utilize heat energy are for power generation, engines and motors, and chemical processing.

Most power plants generate electricity by heating water to produce steam that spins a turbine connected to a generator. This thermal power generation relies on heat sources like coal, natural gas, nuclear fission, and even concentrated solar power. Without harnessing heat energy, we wouldn’t have access to electricity in our homes.

Heat engines like internal combustion engines in cars and heat motors like steam turbines also depend on heat energy. Burning gasoline in a car engine converts chemical potential energy into heat which expands gases to push pistons. Heat from burning fuel creates pressurized steam to spin turbines connected to generators. Thermal power drives mechanical motion in many essential machines.

Heating and cooling is important in chemical processing for industries like oil refining, plastics manufacturing, and food processing. Carefully managing heat energy can break down or combine molecules for producing chemicals, fuels, materials, pharmaceuticals, and more. Much of modern industry relies on heat transfer processes.

Heat in Earth Systems

The Earth itself produces a tremendous amount of heat energy from within through naturally occurring geothermal energy. This heat comes from radioactive decay in the planet’s core and mantle as well as leftover heat from the Earth’s formation billions of years ago. This geothermal energy manifests itself through hot springs, geysers, and volcanic activity. It also heats underground water reservoirs that we tap for geothermal power generation.

Solar radiation from the Sun is the primary driver of weather and climate patterns on Earth. The greenhouse effect, caused by gases like carbon dioxide and methane, helps trap some of the Sun’s warmth in the atmosphere. However, human activities like burning fossil fuels have increased the greenhouse effect, causing global temperatures to rise.

Rising global temperatures are profoundly impacting Earth systems. Glaciers and polar ice caps are melting at accelerated rates, causing sea levels to rise. Weather phenomena like hurricanes are becoming more intense due to warmer oceans. Climate zones are shifting, affecting ecosystems and growing seasons. Droughts, wildfires, floods, and extreme heat waves are becoming more frequent.

Understanding the natural flow of heat energy on Earth and the influence of human activity is crucial for making policies to mitigate climate change risks and build resiliency. Teaching kids about these scientific processes can inspire them to be good stewards of the planet.

Heat in Outer Space

Outer space may seem cold and empty, but there is a tremendous amount of heat energy out there! The biggest source of heat in space is stars like our Sun. The Sun’s core reaches temperatures of over 15 million degrees Celsius. Through nuclear fusion reactions, the Sun generates unimaginable amounts of heat and light energy. This energy radiates outward across space, with a small fraction reaching Earth about 150 million kilometers away. Without the heating effect of the Sun, Earth’s surface would be a frigid -18°C. The Sun’s heat helps power life, weather, climate, and ocean currents here on Earth.

Other stars also produce heat through nuclear fusion in their cores. The color and brightness of a star depends on its surface temperature. Cooler red dwarf stars may have surface temperatures around 2500°C. Hot blue giant stars burn at over 10,000°C. The total heat energy radiating from all the stars in space is astounding.

Luckily, Earth’s atmosphere acts like a thermal blanket, absorbing heat energy from the Sun and insulating the planet from the frigid temperatures of outer space. The atmosphere keeps Earth’s average surface temperature a comfortable 15°C. So while space itself is cold at -270°C, the Sun and other stars fill it with heat energy that allows life in the universe to thrive.

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