Heat

1. HEAT

2. WHAT IS HEAT? Heat is a form of energy that makes things feel warm or hot. It’s the energy that moves from one object to another when they have different temperatures.

3. HoT AND COLD Hot and cold are words we use to describe how things feel to us based on their temperature—a measure of how much heat energy something has.

4. TEMPERATURE Temperature is a way to measure how hot or cold something is. It tells us how much heat energy an object has. For example, a boiling pot of water has a higher temperature than a glass of ice water because it has more heat energy.

5. thermometer A thermometer is a device used to measure temperature, which tells us how hot or cold something is. It works by detecting changes in heat and showing them as a number in specific units.

6. There are several types of thermometers based on what they measure and how they work: • Liquid-in-Glass Thermometer: Uses liquid (usually mercury or alcohol) that expands and rises in a tube as the temperature increases. • Common for measuring body temperature or room temperature

7. Digital Thermometer: • Uses electronic sensors to measure temperature and displays it on a digital screen. • Widely used for body temperature, weather, and industrial purposes. • Infrared Thermometer: Measures heat emitted by objects and converts it to a temperature reading without touching the object. Uses: For checking body temperature, hot surfaces, or during COVID-19 for contactless measurements.

8. Units of Temperature: • Thermometers display temperature in one of three main units: • Celsius (°C) • Most commonly used around the world. • Water freezes at 0°C and boils at 100°C. • Fahrenheit (°F) • Used mainly in the United States. • Water freezes at 32°F and boils at 212°F. • Kelvin (K) • Used in science and research. • Starts at absolute zero (0 K), the point where particles stop moving entirely. • To convert from Celsius to Kelvin: Add 273.15 (e.g., 0°C = 273.15 K).

9. HEAT TRANSFER Heat is energy that moves from one object to another because of a temperature difference. It always flows from the hotter object (higher temperature) to the colder object (lower temperature) until both objects reach the same temperature, a state called thermal equilibrium.

10. There are three primary types of heat transfer: conduction, convection, and radiation. Each works differently and occurs in specific scenarios.

11. Conduction • How It Works:In conduction, heat transfers through direct contact between particles of a solid, liquid, or gas. The heat moves from a region of higher temperature to a region of lower temperature as particles collide and transfer energy. • Where It Happens:Conduction is most effective in solids, especially metals, which have tightly packed particles that can transfer heat quickly.

12. Examples: A metal spoon getting hot when placed in a cup of hot tea. Heat moving through the walls of a heated room on a cold day. Key Feature:The rate of conduction depends on the material's thermal conductivity (metals like copper are good conductors, while wood and plastic are poor conductors or insulators). • Convection • How It Works: • Convection occurs in fluids (liquids and gases). Heat causes the fluid to expand, become less dense, and rise. Cooler, denser fluid then sinks, creating a circulating flow called a convection current.

13. Where It Happens:Convection is common in liquids and gases where particles can move freely. • Examples: • Boiling water: Hot water near the bottom rises, and cooler water sinks. • Warm air rising from a heater or cool air sinking near a window. • Ocean currents and weather patterns like wind. • Key Feature:Convection is responsible for large-scale heat transfer, like in the atmosphere and oceans.

14. Radiation • How It Works:Radiation transfers heat through electromagnetic waves, such as infrared waves. Unlike conduction and convection, radiation does not require a medium (like air or water) and can occur in a vacuum. • Where It Happens:Radiation happens everywhere and is most noticeable when there is a heat source emitting energy.

15. Examples: The warmth of the sun reaching Earth through space. Feeling the heat from a fire without touching it. A microwave oven heating food. Key Feature:Dark or dull surfaces absorb more radiant heat, while shiny surfaces reflect it.