Reference Frame of Describing Motion

A reference frame is how we define what is “stationary.”
We define the frame of reference as stationary.
All positions of measurement are made from a frame of reference.
The most common reference frame is the Earth.

Trains and speed

Trains are useful for thinking about reference frames.
If we use the train as our reference frame,

• the station moves
• the train is stationary

If a train station is our frame of reference,

• the train moves
• the station is stationary

Maps and position

Maps are useful for thinking about coordinate systems.
“Sydney is 70 km away” is a useless direction to have on a map.
A map would need to have a reference point to start at.
“Sydney is 70 km North of Wollongong” is far more useful.

Coordinate systems

A common way of measuring position is with a coordinate system.
These systems may be 1D, 2D, or 3D.
Coordinate systems are usually stationary.
The origin of the coordinate system is where an object’s position is (0,0,0).

Using different coordinate systems

Changing coordinate systems will change the measurements taken.
The distance between two positions stays the same regardless of an observer’s frame of reference.
The same is true for differences in speed.