Energy

All systems harness some form of energy. We define energy as the capacity to do work or cause change.

At it's most simple, we group energy as kinetic or potential. The examples provided are not exhaustive.

Kinetic Energy

Kinetic energy is energy in motion. Types of energy within this category include mechanical, electrical, thermal, radiant, and sound.

Potential Energy

Potential energy is stored energy. Types of energy within this category include chemical, nuclear, gravitational, and elastic.

The Law of Conservation of Energy

The law of conservation of energy is quite simple, and states that energy cannot be created or destroyed; it can only be converted to one form or another. The energy in the universe is constant.

This means we can harness energy, but cannot create it.

Converting Energy

As the law of conservation of energy states, energy can be changed from one form to another. For example, within a car, chemical energy is converted to heat energy, which is converted to mechanical energy that pushes the pistons. The reciprocal movement from the pistons is converted to rotational movement, which is harnessed in the wheels, causing the car to move. Energy conversion is never 100% efficient, and energy will always be lost in the conversion process, to sound, heat, or other forms of energy.

Measuring Energy

The standard SI unit for measuring energy is joules (J). A single joule is quite a small amount of energy. For example, to lift an average apple up 1m into the air would take roughly 1J of energy. As such, it is very common to see joules expressed in kilojoules (kJ) and megajoules (MJ).

$$1\,\text{kJ} = 1000\,\text{J}$$ $$1\,\text{MJ} = 1000\,\text{kJ}$$

In Systems Engineering, the equation we use for measuring energy is:

$$\text{Energy} = \text{Power} \times \text{time}$$

Time is measured in seconds. Power is the transfer of energy, and will either be mechanical power, which is calculated as:

$$\text{Power} = \frac{\text{work done}}{\text{time}}$$

or electrical power, and calculated as:

$$\text{Power} = \text{voltage} \times \text{current}$$

Power is measured in watts (W), and $1\,\text{W} = 1\,\text{J/s}$

There are a lot of concepts here that will be unpacked in other sections.