Thermal Energy Transfers Chapter Notes | Science for Grade 6 PDF Download

Introduction

Thermal energy is the energy that makes things hot or cold. This chapter helps us understand how thermal energy moves from one object to another, like when hot toast cools down on a plate or when water heats up in a microwave. We will learn about different ways thermal energy transfers, such as conduction, convection, and radiation, and how these processes work in everyday life and in nature. By studying this, we can see how energy flows in systems and why things like food or water change temperature over time.

Where does thermal energy go?

Systems and Energy

• A system is a group of objects that work together, like water in beakers or a microwave with food.
• Energy moves between objects in a system.
• A closed system does not share energy or matter with the outside environment, like a microwave heating food.
• In reality, no system is fully closed because some energy always moves to or from the environment.
• An open system allows energy and matter to move in and out, like hot water cooling in a beaker.
• The source object gives energy during a transfer, like hot toast.
• The receiver object gains energy, like a plate under the toast.

Direction of Thermal Energy Transfer

• All objects have thermal energy because their particles are moving.
• Thermal energy moves from objects with higher temperatures to objects with lower temperatures. This movement of energy is called heat.
• You cannot make something colder by adding "coldness"; it cools by losing energy to a cooler object.
• For example, water in an ice cube tray at 10°C loses energy to a freezer at 0°C to freeze.

Conduction

• Conduction is when thermal energy moves between objects that touch each other.
• It happens because particles in the hotter object bump into particles in the cooler object.
  • For example, when hot toast touches a plate, the plate gets warmer.
• Particles with more energy (faster-moving) give energy to particles with less energy (slower-moving).
• When one particle loses energy, it slows down, and the other particle speeds up.
• Conduction can happen in solids, liquids, and gases.

Thermal Equilibrium

• When two objects in contact have the same temperature, they are in thermal equilibrium.
• In thermal equilibrium, particles still bump into each other and share energy, but the average energy stays the same.
• For example, water in a beaker and the air around it reach the same temperature after a long time.

How does thermal energy transfer when objects are not in contact?

• Radiation is when thermal energy moves through electromagnetic waves, like light or heat from the Sun.
• All objects, like the Sun, fire, or even people, give off thermal energy through radiation.
• Warmer objects give off more radiation than cooler ones.
• A thermogram is a picture that shows radiation using colors: white, red, and yellow for hot objects, and blue, purple, or black for cooler ones.
• Radiation can transfer energy through empty space, like from the Sun to Earth, because space has little matter.
• Radiation also works in solids, liquids, and gases, unlike conduction, which needs contact.

Did You Know?

Thermal energy from the Sun reaches Earth through radiation because space is a vacuum with very little or no matter. Since conduction needs direct contact between objects, it can't happen in space. That’s why radiation is the only way thermal energy can travel across space. Interestingly, radiation can also transfer heat through solids like rocks, liquids like ocean water, and even gases in the atmosphere!

How else does thermal energy transfer in liquids and gases?

• Convection is when thermal energy moves because particles in a liquid or gas flow from one place to another.
• Hot particles rise because they are less dense, and cooler particles sink because they are denser.
• For example, air heated by a toaster rises, making the area above it warmer than the sides.
• Convection only happens in liquids and gases, not solids, because particles in solids cannot flow.

Did You Know?

Convection is a key process that helps cycle materials through Earth’s systems. It causes water to move and circulate in oceans and other water bodies. Convection also helps move air across Earth’s surface and even drives the movement of hot magma deep inside the Earth!