Define the unit joule.

Explanation

To define the unit joule, we can break down the explanation into clear and concise steps:

### Step-by-Step Solution:

1. **Definition of Joule**: The joule (symbol: J) is the SI unit of work, energy, and heat.

2. **Understanding Work**: Work is defined as the product of the force applied to an object and the displacement of that object in the direction of the force. Mathematically, it is expressed as:
\[
...