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• Energy can transfer by heating from a hotter region to a cooler region.

• The temperature of the hotter region decreases. The temperature of the cooler region increases.

• Heating can occur by conduction, radiation or convection.

The hotter an object, the more energy it has in its thermal energy store .

The average speed of particles in a hot substance is greater than in a cold substance.

Temperature is how hot a substance is. Temperature is commonly measured in degrees Celsius (°C) using a thermometer.

Temperature depends on the average speed of the particles in a substance.

Example - a hot cup of tea cools down

Temperature

The cup of tea has an initial temperature of 80°C and cools to a temperature of 30°C . Energy has transferred to the surroundings.

Thermal energy store

Hot tea has more energy in its thermal energy store than cold tea. As the tea cooled, the average speed of the particles in the tea reduced.

This energy didn’t disappear - it transferred to the surroundings.

Energy has transferred from the thermal energy store of the tea to the thermal energy store of the surroundings.

If there is a difference in temperature between two objects, energy transfers by heating from the hotter object to the cooler one.

The greater difference in temperature, the faster the energy is transferred.

Example 1 - eating an ice lolly on a hot day

Energy is transferred by heating from the hot surroundings to the cold lolly. This causes the lolly to warm up.

Example 2 - drinking a hot coffee on a cold day

Energy is transferred by heating from the hot coffee to the cold surroundings. This causes the coffee to cool down.

When the objects reach the same temperature as the surrounding environment, the energy transfer will stop.

When the objects are at the same temperature, they are in thermal equilibrium.

Energy is transferred by heating due to:

• radiation

• conduction

• convection

Watch the video to find out more about radiation, conduction and convection.

All objects transfer energy to their surroundings by infrared radiation. The hotter the object, the more infrared radiation it emits.

Infrared radiation is a type of electromagnetic wave. Unlike conduction and convection, there are no particles involved. This means that energy can be transferred by radiation when there are no particles, like the vacuum of space.

Radiation is why we feel the warmth of the Sun.

Thermal imaging cameras detect the amount of infrared radiation emitted by an object.

The camera produces an image like this one of the hand.

The blue and purple areas represent cooler areas. These emit less infrared radiation.

The yellow and orange areas represent hotter areas. These emit lots of infrared radiation.

Conduction is where energy is transferred by the vibrating particles in a substance. The energy is transferred from a hotter region to a cooler region.

Conduction happens fastest in solids because the particles are close together.

Materials which transfer energy easily from a hot area to a cooler area by conduction are called conductors. Metals are very good conductors.

Have a look through this slideshow to understand more about metals as conductors.

Materials which do not transfer energy easily from a hotter area to a cooler area are called insulators. Air and plastics are good insulators.

The best insulator is a vacuum. Conduction cannot occur if there are no particles.

A fluid is a substance that can flow. Both liquids and gases are fluids.

The particles in a fluid can move around from one place to another.

Look through the slideshow to understand more about the stages of convection.

Insulation is used to reduce unwanted thermal energy transfers and maintain the temperature of an object.

For example, an insulated picnic bag can keep your lunch cooler for longer. It can also keep hot food hotter for longer.

The table shows how conduction, radiation and convection transfer energy and how to reduce the method of energy transfer.

Look at these examples to understand how conduction, radiation and convection can be reduced in a range familiar objects and places.

Insulated coffee cups

Insulated coffee cups have two layers. There is a gap between the two layers to reduce conduction.

The cup also has a lid. This reduces convection by trapping the hot gases inside the cup.

The inside of the cups are usually a shiny white surface. This reflects infrared radiation.

Cooking pan handles

Cooking pans are made of metal. Energy is transferred to the food by conduction through the metal base and sides of the pan.

Some pans have metal handles and some have plastic handles.

Flasks

Flasks come in many different colours and are used to hold either hot or cold drinks. The colour of the flask is important.

Choose the shiny white flask to keep your water cold. It transfers less energy by radiation. A shiny white surface is a poor absorber of infrared radiation and therefore helps keep a cold drink cold.

The shiny white flask is also the right choice to keep a hot drink hot. It transfers less energy by radiation. A shiny white surface is a poor emitter of infrared radiation and therefore helps keep a hot drink hot.

There are many different examples of insulation used within the home to stop it getting too hot in the summer or too cold in the winter. Look through the slideshow to explore more.

Are you a physics teacher looking for more resources to engage your students? In this series of short films, daredevil science geek Greg Foot is prepared to attempt anything to find your students the answers to some of life's weirder questions.

���˿��� Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.