Heat can be transferred in three main ways: conduction, convection, and radiation. It always flows from hotter objects to cooler ones until temperatures equalise with the surroundings.
Everyday Examples
- A cup of coffee cools down because it gives out heat energy to the environment.
- A cold drink can warm up because it absorbs heat energy from the surroundings.
Conduction
In solids, particles vibrate more when heated. These vibrating particles collide with neighbouring particles, transferring kinetic energy. Metals are the best conductors, solids conduct better than liquids, and gases are poor conductors (they act as insulators).
Atoms are always vibrating. When heated, they vibrate faster, and each collision transfers energy to the next particle. This process allows heat to spread through the solid.
Convection
In fluids (liquids and gases), heating increases particle kinetic energy. The particles spread out, making the fluid less dense. The hot fluid rises above the cooler, denser fluid, creating a convection current.
Examples:
- Hot air rising in cooler air.
- Hot water rising in cooler water.
Convection does not occur in solids, since atoms cannot move freely.
Radiation
All objects emit and absorb infrared radiation. The hotter the object, the more radiation it emits. When objects absorb infrared radiation, their temperature increases.
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