Heat and heat transfer
Heat is the transfer of thermal energy from a hotter object to a cooler one because of a difference in temperature. Unlike temperature, which measures how hot or cold something is, heat is energy that is always moving until both objects reach the same temperature, a state called thermal equilibrium. Heat can travel in three ways: conduction, where particles pass energy through direct contact; convection, where warm liquids and gases rise while cooler ones sink, creating currents; and radiation, where energy travels as electromagnetic waves and does not need a medium, allowing the Sun to warm the Earth through space. The speed of heat transfer depends on factors such as the material, temperature difference, surface area, and insulation. Metals are excellent conductors because their free electrons carry energy quickly, while materials like wood, plastic, and air are insulators that slow down heat transfer. Heat transfer is responsible for countless natural and everyday processes, from sea breezes and weather patterns to cooking food, melting ice, evaporation, and keeping our homes warm or cool, making it one of the most important forms of energy transfer in science.