Energy Transferred by Working
Energy and Thermal Physics

How to describe processes in terms of energy

Physics Narrative for 11-14 Supporting Physics Teaching

Describing processes in terms of energy

You can develop an energy description using the following approach.

Select a part of the world to study: chose the process or change to analyse.

Define the before and after snapshots for the change that you want to study. If you choose different moments to take your snapshots, you'll end up describing different parts of the process.

Identify the energy stores between which energy is shifted during the process.

A simple example to consider

For example, the action of lifting an ornament onto a shelf and allowing it to fall back to Earth.

For our example, various start and end points are possible, defining two quite separate processes that jointly make up the action:

The lifting process

Start: Ornament on the ground

End: Ornament on the shelf

The falling process

Start: Ornament on the shelf

End: Ornament on the ground

For the lifting process, two energy stores are of interest:

  • The chemical store associated with the lifting arm
  • The gravitational store of the ornament in the Earth's field

Energy is shifted from the chemical store of your muscles to the gravitational store of the ornament in the Earth's field.

The general approach:

  1. Choose a change to study.
  2. Take a snapshot (before).
  3. Take a snapshot (after).
  4. Identify the stores.
  5. Produce an energy description based on this analysis.

Energy Transferred by Working
appears in the relation dU=dQ+dW
is used in analyses relating to Working Engines Thermionic Emission
is a special case of Work
has the special case Potential Energy Kinetic Energy
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