[oblib]

I'll offer this life experience:

I got into a debate with some fellow backpackers a couple years ago about how to measure total distance traveled when hiking in mountainous areas. They all said they could measure the total distance using the Pythagoras theorem but they were only measuring the distances of the angled sides of a triangle, not both the forward and up/down, which you have to traverse in the real world.

When I explained that they were only measuring the distance in a 2D world but since we live in a 3D world we need to measure both forward and up and down to get total distance traveled they were all in agreement that I couldn't be more wrong.

When I tried pointing out that this is an exercise in the physics of spatial dimensions (3D), and not a 2D flat plane, they couldn't (or more aptly put, refused) to grasp the difference.

I think this approach might be another good way to illustrate using it because while they all understood how it worked they didn't have a clue about when to apply it, which your example perfectly illustrates.

[vitaminbandit]

I'm sure they understood exactly what you meant and could apply it. Nobody measures distance the way you described it.