HEAT-TRANSFER of the world in the .pptx

Heat Transfer: A Detailed Explanation
Heat transfer is the process of thermal energy moving from one object to another due to a temperature difference. This energy can be transferred in three main ways:

Conduction – Direct contact
Convection – Movement of fluids
Radiation – Electromagnetic waves
Each method plays a vital role in daily life, natural processes, and industrial applications.

1. Conduction (Heat Transfer by Direct Contact)
Conduction occurs when heat moves through a solid or between objects in direct contact. The heat flows from the hotter region to the cooler one due to the vibration and collision of molecules.

How It Works:
In a solid, atoms and molecules are tightly packed.
When heated, particles vibrate faster and transfer their energy to neighboring particles.
This energy spreads through the material until equilibrium (same temperature) is reached.
Examples of Conduction:
✅ A metal spoon getting hot when placed in a pot of boiling water.
✅ Touching a hot pan and feeling the heat transfer to your hand.
✅ Ice melting in your hand due to heat transfer from your skin.

Factors Affecting Conduction:
Material Type: Metals (like copper and aluminum) are good conductors because they have free electrons that transfer heat efficiently. Insulators (wood, rubber, air) resist conduction.
Temperature Difference: A higher temperature difference leads to faster heat transfer.
Thickness & Surface Area: Thicker materials slow down conduction, while larger surface areas speed it up.
2. Convection (Heat Transfer by Fluid Motion)
Convection occurs in liquids and gases where heat is transferred by the movement of molecules in a circulating flow.

How It Works:
When a fluid (liquid or gas) is heated, it expands, becomes less dense, and rises.
Cooler, denser fluid moves in to replace it, creating a convection current.
This continuous cycle distributes heat.
Types of Convection:
🔹 Natural Convection: Happens due to density changes (e.g., warm air rising).
🔹 Forced Convection: Occurs when an external force (like a fan or pump) moves the fluid.

Examples of Convection:
✅ Boiling water: Hot water rises, cool water sinks, forming a convection current.
✅ Sea breeze: Land heats up faster than water, causing warm air to rise and cooler ocean air to replace it.
✅ Radiators: Heated air rises, cool air falls, creating a cycle that warms a room.

Factors Affecting Convection:
Fluid Properties: Viscosity and density impact how easily convection occurs.
Heat Source Strength: A stronger heat source increases convection currents.
Gravity: It plays a role in density-driven natural convection.
3. Radiation (Heat Transfer by Electromagnetic Waves)
Radiation transfers heat without needing a medium (solid, liquid, or gas). Instead, energy is emitted as electromagnetic waves, primarily infrared radiation.

How It Works:
Hot objects emit thermal radiation.
The waves travel through space and can be absorbed, reflected, or transmitted by other objects.
Dark, rough surfaces

1. HEAT TRANSFER SCIENCE - GRADE 7

2. THERMAL ENERGY Thermal energy refers to the energy contained within a system that is responsible for its temperature. When thermal energy is transformed, heat is always produced.

3. HEAT Heat is the flow of thermal energy. Also called an energy in transit .

4. HEAT TRANSFER Hotter Cooler The heat energy transfers from a hotter substance to a cooler substance. The transfer of energy is due to temperature difference of objects.

5. Marshmallow becomes hotter, the heat flowed from the flame of the burning wood which has a higher temperature to the marshmallow which has a lower temperature. The transfer of heat will stop when both object reach the same temperature. REMEMBER

6. 3 METHODS OF HEAT TRANSFER CONDUCTION CONVECTION RADIATION

7. CONDUCTION Conduction takes place between objects with different temperatures that are in contact with each other, but it is dominant in solids only . Heat flows from the warmer to the cooler object until they are both at the same temperature.

8. CONDUCTION

9. CONDUCTION The heat from the stove makes the pan hot. The heat from the hot coffee makes the mug hot.

10. CONDUCTION Materials that conduct heat well are called thermal conductors (good conductors) such as metals like copper, iron, aluminum, steel, silver, brass, lead etc. Whereas materials that conduct heat poorly are known as thermal insulators (poor conductors) some examples are non-metals like wood, rubber, plastic, glass, paper etc.

11. CONVECTION Convection is the transfer of heat energy by means of the moving molecules of liquids or gases . When the molecules of the liquid or gas is heated, it’s density decreases causes it to rise and pushed the cooler molecules which is denser to take its place at the bottom.

12. CONVECTION

13. RADIATION Radiation is a transfer of heat energy through space in the form of electromagnetic waves. It is a method of heat transfer that does not need any contact between the heat source and the heated object . Heat from the sun reaches the earth through radiation.

14. RADIATION

15. HEAT TRANSFER

16. HEAT TRANSFER

17. HEAT TRANSFER SCIENCE - GRADE 7

18. REVIEW

19. How do materials gain positive charge? by gaining electrons CHARGES by losing electrons

20. How do materials gain positive charge? by gaining electrons CHARGES by losing electrons

21. How do materials gain negative charge? by gaining electrons CHARGES by losing electrons

22. How do materials gain negative charge? by gaining electrons CHARGES by losing electrons

23. 3 Types of Charging Processes FRICTION CONDUCTION INDUCTION

24. Also known as charging by rubbing When an object is rubbed, it will gain or lose electrons and will gain a positive or negative charge. CHARGING BY FRICTION

25. CHARGING BY FRICTION

26. electrons transferred by direct contact. electrons move from one object to another. CHARGING BY CONDUCTION

27. The rearrangement of electrons caused by charged object placed near but not touched to a neutral object. Charge is “induced” when electrons move away, or attract. CHARGING BY INDUCTION

28. REVIEW

29. DISTANCE VS. TIME GRAPH What is plotted in the x axis? What is plotted in the y axis? What the vertical line represent?

30. Distance vs. Time Graph Interpretation NOT MOVING CONSTANT SPEED

31. Distance vs. Time Graph Interpretation NOT MOVING CONSTANT SPEED

32. Velocity vs. Time Graph Interpretation CONSTANT SPEED ACCELERATING OR SPEEDING UP DECELERATING OR SLOWING DOWN

33. Velocity vs. Time Graph Interpretation CONSTANT SPEED ACCELERATING OR SPEEDING UP DECELERATING OR SLOWING DOWN A B C D E