Physics
Energy Flow
Quick fact
In every energy conversion, about 90% of the energy is dissipated as heat, meaning the universe is constantly 'spreading out' energy.
Why this is interesting
Every action, from a single heartbeat to a roaring thunderstorm, relies on a continuous stream of energy. But where does this energy come from, and where does it go?
Read the full explanation
Understanding Energy Flow
Think of energy like water flowing downhill. It always moves from a place of higher concentration to lower concentration. In an ecosystem, energy starts with the sun, which plants capture through photosynthesis. When animals eat plants, they take in that stored chemical energy, but only about 10% of it transfers to the next level—the rest is lost as heat during life processes. This same principle applies everywhere: a car engine converts chemical energy into motion, but much of it becomes heat. Energy never disappears; it just changes form and spreads out.
A deeper explanation
At the core of energy flow are the laws of thermodynamics. The first law states that energy is conserved—it cannot be created or destroyed, only transformed. The second law says that in any transformation, the total entropy (disorder) of the universe increases. This means that whenever energy flows or converts, some of it inevitably becomes unusable heat, dispersing into the environment. This is why perpetual motion machines are impossible and why organisms must constantly consume energy to maintain order. Energy flow also explains ecological pyramids: limited energy transfer restricts the number of trophic levels. In technology, understanding energy flow is key to improving efficiency in power plants, engines, and electronic devices.