Heat

Heat is a form of energy that flows from hot to cold. Temperature is the measure of hotness/coldness. Unit: Celsius (°C), Kelvin (K), Fahrenheit (°F). Thermometer measures temperature. Clinical thermometer: 35-42°C range (for human body). Laboratory thermometer: -10 to 110°C. Body temperature: 37°C (98.6°F) is normal.

CONDUCTION: heat transfer through solid materials by contact. Metals conduct well (good conductors) — iron, copper, aluminium. Wood, plastic are poor conductors (insulators). CONVECTION: heat transfer in liquids and gases — hot fluid rises (less dense), cold falls (more dense), creating convection currents. Basis of sea breeze, boiling water, hot air balloons.

Heat transfer without any medium (works in vacuum). Energy travels as infrared waves (electromagnetic radiation). Sun heats Earth through radiation across empty space. Dark/dull surfaces absorb more radiation. Shiny/light surfaces reflect more. That's why we wear light clothes in summer and dark in winter. Thermocol and wool trap air — excellent insulators (no convection).