Science & Technology — Force and Energy

Subtopic: Heat energy (for age 9, Kenya)

Learning goals:

• Know what heat energy is.
• Identify common sources of heat in Kenya.
• See how heat moves (conduction, convection, radiation).
• Do a simple, safe experiment with ice melting.

What is heat energy?

Heat energy (also called thermal energy) is the energy that makes things feel hot. When something gets hotter, its tiny particles (atoms and molecules) move faster. Heat moves from hotter places to colder places.

Common sources of heat (Kenyan examples)

• Sunlight — warms our bodies and dries maize and clothes.
• Fire — cooking on a jiko or over a firewood stove produces heat.
• Charcoal and kerosene stoves — used for cooking in many homes.
• Electric stoves and kettles — in towns and some homes.
• Friction — rubbing two sticks together makes heat (used to start fires).
• Geothermal hot springs — underground heat that appears at the surface.

How heat moves

1. Conduction — heat moves through touching. Example: a metal spoon gets hot from the hot tea.

2. Convection — heat moves in liquids and gases when warm parts rise and cool parts sink. Example: boiling water in a pot.

3. Radiation — heat travels in straight lines through space. Example: the Sun warms your skin even though space is between you and the Sun.

Changes of state with heat (simple)

• Melting — solid to liquid (ice to water) when heated.
• Evaporation — liquid to gas (water to vapour) when heated.
• Condensation — gas to liquid (steam cools to water).
• Freezing — liquid to solid (water to ice) when cooled.

Simple experiment: Watch ice melt

Materials:

• Three small bowls or plates
• Ice cubes (same size)
• Warm water, room temperature water, and cool water
• Clock or watch

Steps:

1. Put one ice cube in each bowl.
2. Pour warm water into the first bowl, room temperature water into the second, and cool water near the third (or leave one in air).
3. Watch and time how long each ice cube takes to melt.

What you should see: The ice in the warm water melts fastest. Heat from the warm water goes into the ice and makes it melt.

Safety rules

• Ask an adult before using fire, hot water or an electric kettle.
• Keep hands and face away from flames and hot pots.
• Wear gloves or use a cloth when touching hot pans.

Fun facts

• The Sun gives us heat by radiation — it travels through space!
• Wood ash and some dark objects warm faster in the sun because they absorb heat well.
• In Kenya, the Great Rift Valley has hot springs caused by heat from under the ground (geothermal).

Glossary (simple)

Heat (thermal energy)

Energy that makes things hot.

Conduction

Heat transfer through touch.

Convection

Heat transfer in liquids and gases by movement.

Radiation

Heat transfer through space by rays (no touching needed).

Try: Next time you cook or play outside, think about where the heat is coming from and how it reaches you!