Heat Energy – JSS1 Intermediate Science Lesson Note (Third Term)

WHAT IS HEAT?

Have you ever wondered why a metal spoon left in a hot pot of soup becomes hot enough to burn your hand? Or why you feel warm when you stand near a fire?

Heat is a form of energy that moves from a hot object to a cold object. It is the energy that makes the tiny particles in an object move faster.

Sources of Heat

We get heat from many places:

1. The Sun: This is the primary and most important source of heat for the Earth.
2. Friction: Rub your palms together quickly. Feel that? That is heat caused by two things rubbing together.
3. Electricity: We use this for electric irons, heaters, and cookers.
4. Burning Fuels: Burning wood, coal, gas, or petrol releases heat.
5. Chemical Reactions: Some chemicals produce heat when mixed.

HEAT TRANSFER – CONDUCTION

Heat is “restless”—it always wants to move. It travels in three main ways. The first way is through solids, called Conduction.

How it works:

Imagine a line of students. If the first student wiggles, he bumps into the second, who bumps into the third. Soon, everyone is wiggling! In conduction, heat moves from particle to particle without the material itself moving.

• Conductors: These are materials that allow heat to pass through them easily (like metals—iron, copper, aluminum). This is why cooking pots are made of metal.
• Insulators: These are materials that do not allow heat to pass through easily (like wood, plastic, or rubber). This is why the handles of pots are made of plastic or wood.

HEAT TRANSFER – CONVECTION

The second way heat moves is through liquids (like water) and gases (like air). This is called Convection.

How it works:

In liquids and gases, the particles can actually move around.

1. When you heat water in a pot, the water at the bottom gets hot and becomes “lighter.”
2. The hot water rises to the top.
3. The cooler, heavier water at the top sinks to the bottom to take its place.
4. This creates a “circle” of moving water called a Convection Current.

• Real-life example: This is why an Air Conditioner is placed high up on a wall. The cold air sinks down to cool the room, while the warm air rises to be cooled.

HEAT TRANSFER – RADIATION

The third way heat moves is called Radiation. This is the most special way because it does not need any material (solid, liquid, or gas) to travel through. It can travel through empty space!

How it works:

Heat moves in waves, just like light.

• The Sun: Heat from the sun travels through millions of miles of empty space to reach us on Earth.
• The Fire: If you sit near a campfire, you feel the heat on your face even if the wind is blowing away from you. That is radiation.

Dark vs. Light Colors

• Dark colors (like black): These are good absorbers of radiant heat. This is why you feel hotter wearing a black shirt in the sun.
• Light colors (like white): These reflect heat away. This is why many people in hot countries wear white clothes.

Class Activity

Let’s see if you can identify the type of heat transfer:

1. A spoon in hot tea getting hot: __________
2. The sun warming the ground: __________
3. Smoke rising up a chimney: __________
4. Using a heating coil to boil water: __________

Revision Questions

1. Define heat energy in your own words.
2. Why are the handles of frying pans made of plastic or wood?
3. Explain how a convection current works in a pot of boiling water.
4. Which method of heat transfer does not require a medium to travel?

Homework

Go to the kitchen while someone is cooking.

• Identify one object showing Conduction.
• Explain how Convection is happening in the pot.
• Stand a safe distance from the stove and explain why you can still feel the warmth (Radiation).