# Explain how energy flows through the ecosystem

## One-way street of energy simply explained

The term one-way street of energy is easy to understand when you think of things as simple as melting an ice cube or a ball falling on the floor.

### One-way street, because it only goes in one direction

A one-way street in traffic may not be driven in the opposite direction, but it is of course technically possible to do so. It's the same with energy.

• Energy is not lost in a closed system, but it changes from one energy to another. Example: A ball falls down, the potential energy is converted into kinetic energy.
• This type of energy conversion is not a one-way street because, as you probably know, the ball will bounce and be thrown back up. The kinetic energy is converted into potential energy.
• However, you will quickly notice that the ball does not return to the same position as it was at the beginning. You can use a fine thermometer to determine that the ball becomes warm during the fall from friction in the air and during the impact. If you play squash, you are probably familiar with the phenomenon that a ball becomes warm when it is hit against the wall or the floor with a racket. This energy conversion is a one-way street, because without further use of energy you will not be able to get the ball moving again with heat.

### The flow of energy goes in one direction

To make it clear to yourself that the energy conversion only goes in one direction, you can keep simple everyday processes in mind. You have to be precise about energy conversion, because energy is neither generated nor consumed, rather one type of energy is converted into a more usable type of energy. Example: steam turbine in a power plant. Now to the procedures to illustrate the one-way street:

• The thermal energy is distributed evenly in the system. There is only one direction in which the heat is distributed over the cold. Put an ice cube on a plate. It is heated and melted by the surrounding air. The resulting water warms up to the temperature of the surrounding room. At the end everything is evenly warm.
• Put hot water in a cold cup, the cup will warm up until the water and the cup are at the same temperature. The cup and water give off heat energy to the surrounding space until the temperature is constant everywhere.
• As you know from steam engines, for example, thermal energy can definitely be converted back into kinetic or potential energy, but this requires a thermal gradient. Even with other types of energy conversion, there is always the problem that thermal energy is generated that cannot be used.
• There is no reversal of the process that the thermal energy is evenly distributed, the water does not freeze back to ice, the cup does not become warmer again and does not heat the water. The distribution of energy is therefore a one-way street.

### Thermodynamics and the one-way street of energy

Using the examples from everyday life mentioned, which you can easily reproduce in experiments if you are not familiar with them, you can understand the main principles of thermodynamics.

• 1st main law: The energy of a closed system is constant. Energy is not lost, but it is converted. There is the natural process that the energy form heat is sought and this is distributed evenly.
• 2nd main principle: Thermal energy cannot be converted into other types of energy to any extent. This arises from the fact that heat is inherently evenly distributed in the system. To convert heat into other forms of energy, however, you need a heat gradient.

This is understood as a one-way street of energy.