System & Surroundings

Introduction: System, Surroundings, and Energy Accounting

When it comes to energy, choosing what is the system versus what is the surroundings greatly affects what needs to be accounted for when solving for various values. Choosing certain objects to be apart of the system rather than the surroundings can have an extreme effect on the outcome of said variables, especially when the surroundings do a fairly large amount of work on the system. By definition, a system is a specific part of the universe that we choose to study, while the surroundings are everything else that 'surrounds,' and typically has a significant effect on, the system. This page will analyze how different choices of systems can affect the components of the Energy Principle when relating it to the system.

The Energy Principle

To first understand the impact of the choice of system, it is best to fully understand the Energy Principle. The Energy Principle is based off of the fact that energy is a conserved quantity, meaning that it cannot be created nor destroyed. This definition of the conservation of energy gives the equation:

∆Esystem + ∆Esurroundings = 0

This best shows the idea that since energy is a conserved quantity, systems may only gain/lose energy if the surroundings lose/gain that same amount. This can be pictured in the image below.

The equation can then be arranged by using the fact that the change in energy of a specific system is equal to the work done on the system by the surroundings.

∆Esystem = W

where ∆Esystem = Ef - Ei, making this equation now equal to:

Ef = Ei + W

The above equation will be what will primarily be used when accounting for all energy terms when the choice of system/surroundings changes.

Choice of System

Although physical results are always consistent,

External links

Thinking about Physics Thinking by Professor Michael Schatz [1]

References

Matter and Interactions 4th Edition

Thinking about Physics Thinking

--Gnewville3 (talk) 22:39, 19 April 2016 (EDT)