Brain Makeover #2. The energy of a closed system is conserved, but energy always goes from more useful to less useful forms.
Professor James Trefil (author of Science Matters, Why Science?, and 30 other books on science literacy) identified 18 key science concepts every adult should know to be a science literate. We’re here to reintroduce adults to science, in a fun way! It’s all part of our Brain Makeover project to increase adult science literacy. Here’s concept #2, presented by Danielle and explained by Professor James Trefil. We’ll post one each week (more or less) and it to the Brain Makeover collection.
The Energy of a Closed System is Conserved, but energy always goes from more useful to less useful forms.
You do work when you exert a force over a distance (think of pushing a heavy piece of furniture over the floor). Energy is defined as the ability to do work (i.e. to exert a force over a distance). Power is the amount of work done (i.e. the amount of energy expended) divided by the time it takes to do the work.
There are three important things you need to know about energy: (1) it comes in many forms, (2) it can be changed form one form to another, and (3) the total amount of energy in a closed system cannot change (in the language of physicists, it is conserved).
There is energy associated with motion (kinetic energy)—think of a moving train exerting a force on something it hits. There is energy associated with position – think of a rock balancing on a hilltop. There is energy associated with arrangements of electrons in atoms—think of the energy in the gasoline in your car. There is energy associated with heat, which is actually the kinetic energy of moving atoms. There are many other forms, but you get the idea.
When an archer draws a bow, she changes the chemical energy in her muscles to elastic energy in the bent bow. When she releases the arrow, that energy becomes the kinetic energy of the moving arrow, and that energy becomes heat when the arrow pushes into the target. Energy is always changing from one form to another.
No matter what you do, however, no matter how much you change the form of the energy, the total amount stays the same. This is called the First Law of Thermodynamics.
There is an additional fact about energy that deals with the direction of the universe. Heat, left to itself, always flows in one direction—from hot to cold. In the same way, systems left to themselves always become more disordered. This is called the Second Law of Thermodynamics.