Slope and other stuff in math

Hi 

I have been helping my son understand "slope" in math which he was capable of learning. The problem is that he generally does not understand why he should be learning this.

So I tried to search on the internet "brilliant things that slope is used for" and other such criteria but found nothing of interest.

So I was wondering if Khan Academy could do short videos of random math that kids learn and try and sell them why they should learn this.

For instance the video should not explain how to calculate slope but rather what practical things can you accomplish by understanding "slope".

I often run into this problem when helping him with math, that is to explain why he should learn this and that.