Humans
spend hours preening themselves in mirrors and, given half the chance, apes,
elephants, and dolphins would do too. Reflections in mirrors are amazing things
that tell us literally (and psychologically) a great deal about how we see
ourselves. Nowadays, we have mirrors that come with mirror defogger
If
you're a fan of recycling, you will love one of the most fundamental scientific
laws in the universe called the conservation of energy. The basic idea is
really simple: you can't make energy out of thin air or throw it away. It
doesn't matter what you do or how hard you try, you can never create energy or
destroy it: the best you can do is to convert it into a different form, recycle
it, if you prefer. Think what happens when you switch on an electric lamp,
you're not creating light from nothing.
The light is being made from electricity flowing into your home from a power plant. But even a power plant doesn't make energy: it extracts energy locked in a fuel such as oil or coal and turns it into electricity. Energy always has to come from somewhere and go somewhere. If you kick a football, potential energy stored in your muscles is transferred into the ball and makes it fly through the air with kinetic energy. When the ball rolls over the ground, friction (the rubbing force between the ball and whatever it touches) steals away its energy and brings it to rest.
The conservation of energy is the reason why you can't build a machine that will run by itself forever (known as a perpetual motion machine). It's also the reason why your car inevitably runs out of petrol and why you always get an electricity bill coming through your letterbox every few weeks. Now, when you stand in front of a mirror defogger, what you see is the conservation of energy in action, working its magic on light. Light is energy traveling at high speed (300,000 km or 186,000 miles per second) and, when it hits an object, all that energy has to go somewhere? There are three things that can happen when light hits something: it can pass through (if the object is transparent), sink in and disappear (if the object is opaque and darkly coloured), or it can reflect back again (if the object is shiny, light-coloured, and reflective). Either way, the conservation of energy is at work: there is just as much energy around before light hits something as afterward, though some of the light may be converted into other forms.
The light is being made from electricity flowing into your home from a power plant. But even a power plant doesn't make energy: it extracts energy locked in a fuel such as oil or coal and turns it into electricity. Energy always has to come from somewhere and go somewhere. If you kick a football, potential energy stored in your muscles is transferred into the ball and makes it fly through the air with kinetic energy. When the ball rolls over the ground, friction (the rubbing force between the ball and whatever it touches) steals away its energy and brings it to rest.
The conservation of energy is the reason why you can't build a machine that will run by itself forever (known as a perpetual motion machine). It's also the reason why your car inevitably runs out of petrol and why you always get an electricity bill coming through your letterbox every few weeks. Now, when you stand in front of a mirror defogger, what you see is the conservation of energy in action, working its magic on light. Light is energy traveling at high speed (300,000 km or 186,000 miles per second) and, when it hits an object, all that energy has to go somewhere? There are three things that can happen when light hits something: it can pass through (if the object is transparent), sink in and disappear (if the object is opaque and darkly coloured), or it can reflect back again (if the object is shiny, light-coloured, and reflective). Either way, the conservation of energy is at work: there is just as much energy around before light hits something as afterward, though some of the light may be converted into other forms.
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