How to play Train Track
- Choose a mission. Read where the origin is and which way +x points.
- Use the gaps between stations to find the start position xᵢ and the final position x_f.
- Type the final position and the displacement Δx = x_f − xᵢ, with their signs, and press Play.
- When the train arrives, move the origin or flip +x. Watch which numbers change and which do not.
Position needs a reference point
A position is a signed number that says where something is, measured from a chosen origin along a chosen positive direction. Change the origin and every position changes. Displacement, Δx = x_f − xᵢ, is the change in position: it depends only on where the motion starts and ends, so moving the origin never changes it. Its sign tells the direction of the change, and its size is how far the end is from the start in a straight line.
A focused learning model
The track is straight, so one number is enough to give a position. The train is treated as a point that runs at a constant 20 m/s from one station to the next, with no acceleration or braking. Positions are rounded to the nearest metre on screen. Playback runs 5 times faster than real time.