Physics pt.1: Reperesenting Motion

Units 

Let's start with units, units are a type of measurement usually for position (meters), mass (Kilograms) and motion (Meters per second), let's say you have a cat that's 25 units tall, and a swimming pool that's 45 units wide. Well, that doesn't make sense, how can a cat be bigger than a pool, that's where units of measurement come into play, the main two systems the world uses are the metric and imperial systems, both very valid forms of measurement (although 95% of the world uses metric).

When comparing data (weight, height, length), try to stick to one system for measuring to make the comparisons easier to understand. 
For example, for the cat analogy, we can say the cat is 25 centimetres tall, as that is a unit of measurement we are familiar with, and for the pool, we can say that it is 45 meters long and we are easily able to understand what that means. 

Since there are two forms of measurement things can get confusing, there was once a rocket ship (the Mars Climate Orbiter around 125million USD) that due to a measuring mistake, exploded when landing on Mars.

Frames of reference:

These are so that people are on the same page when talking about subjects in physics, for example: Let's say a blue car is travelling right at 45 kilometres per hour, and you standing still on the ground, it will look like the car is whizzing by you at 45 km.
Now that that same scenario but instead of being on the ground stationary, I put you in a yellow van that's going 40km, it will feel like the blue car isn't going very fast, which makes sense as the person standing on the ground and the person in the Yellow van is watching from a different Frame of reference.
We would write this as "The blue car is going, to the view of the Yellow car at 5km"