What is a System? • A system is a set of interacting or interdependent components forming an integrated whole. • Systems share common characteristics, including: • A system has structure, it contains parts that are directly or indirectly related to each other • A system has behavior, it contains processes that transform inputs into outputs • A system has interconnectivity: the parts and processes are connected.
SYSTEMS Examples of systems: • Ecosystems, weather systems, food production systems, sewage treatment systems, photosynthesis, education systems, information distribution systems, your body………
All systems have: • Inputs • energy or materials or both • Outputs • energy, materials or both • may be useful – ex. a crop • may be a problem –ex. pollution
When a system is in equilibrium: • inputs = outputs • Ex. The temperature of our planet will remain constant, provided thatenergy inputs = energy outputs. • If we reduce the outputs of energy by increasing levels of greenhouse gases which trap heat energy, the temperature rises (global warming).
Systems and the Laws of Thermodynamics • The First Law of Thermodynamics tells us: • “Energy is never created or destroyed, only changed from one form to another” Think of a food chain……
Systems and the Laws of Thermodynamics • The Second Law of Thermodynamics tells us that all energy changes release some energy as heat, and eventually all the energy in the universe will have turned to low grade heat energy. A very happy thought… • Again think of a food chain……
Feedback mechanisms in systems • feedback occurs when the output of a system influences the inputs and hence affects the state of the system • positive feedback changes a system to a new state. In most natural systems it is considered a bad thing, but it is not always so! The term “vicious cycle” usually refers to positive feedback.
Positive Feedback examples • Ex. A common example occurs during conferences when a microphone gets too much sound from a speaker. The speaker sound is amplified, resulting in even more speaker sound to the microphone. The sound level quickly increases in volume, eventually overdriving the amplifier, resulting in that awful squeal we all hate. -Ex. teacher encourages student with positive feedback comments on his/her work; student associates learning with being praised so wants to learn more and produces a higher standard of work (a new state!). Student gains confidence from achievement, passes exams and leaves for university.
Feedback mechanisms in systems • negative feedback returns a system to its original state. In many natural systems homeostasis acts as a form of negative feedback . In most natural systems, negative feedback is considered a good thing, because it restores equilibrium, it promotes a steady state.
Negative Feedback Examples - Ex. As the number of rabbits increases in a natural area, there is more food for predators, resulting in an increase in the number of predators. This increase causes a decrease in the number of rabbits, resulting in fewer predators. The result is that the ratio of rabbits to predators is nearly constant.