Energy and its changes

Energy does not disappear; it changes from one kind into another. When we switch on a lamp, electrical energy changes into light (and some heat). When we rub our hands, mechanical energy changes into heat and the palms warm up. A dark shirt or car roof warms in the sun: light energy changes into heat. When we turn the handle of a dynamo, mechanical energy becomes electrical energy and a lamp lights. Water spins the turbine of a hydroelectric station and makes electricity. There are changes inside the human body too: food energy becomes movement in muscles and heat that warms the body. A magnifying glass can focus sunlight onto one spot and set paper on fire, so we never point it at things in the sun and never look at the Sun through it.