Energy is the ability to do work, needed for all activities such as moving, cooking, lighting, heating, and running machines. Major sources of energy include the Sun, water, wind, coal, oil, gas, wood, and food. Forms of energy include light, heat, sound, and electrical energy. Energy can be transformed from one form to another — for example, in hydroelectricity, kinetic energy of flowing water turns into electrical energy, and in a thermal power station, burning fuel produces steam that runs turbines to generate electricity. Windmills use wind to turn blades connected to a generator to make electricity. Light energy allows us to see, and phenomena like reflection (light bouncing back) and rainbows (sunlight splitting into seven colors) show how light behaves. Energy conservation means using energy wisely to avoid waste, such as turning off unused lights and appliances. Electrical energy can be used in devices like fans, TVs, and bulbs, which often transform it into light, sound, or heat. Conductors allow electricity to pass (e.g., metals) while insulators block it (e.g., plastic, rubber). Without the Sun’s heat energy, life on Earth could not survive.