In another post we talked about Root Position Chords.
A root position chord is a very stable chord. It’s like a pyramid. 
You can play a root position chord all day and it doesn’t feel like it needs to go anywhere.
An inversion of a chord is different though. Let’s use the C chord as an example again.
C – E – G These are the notes in the C major triad.
Here are the notes in the C Major Scale. C – D – E – F – G – A – B – C
The C is the first note, or First Degree of the scale. The D is the second note, or Second Degree of the scale, and so on.
C D E F G A B C
1 2 3 4 5 6 7 8
You can see here that C – E – G, is 1 – 3 – 5 in the C major Scale. We call the 1, the Root, the 3, the third (3rd), and the 5, we call the fifth (5th).
Root Position - When the root of a chord is in the bass this is a very stable chord. 
1st Inversion – When the 3rd of a chord is in the bass, it is called a 1st inversion. A C chord with an E in the bass is a 1st inversion chord. C/E
When we hear this kind of chord we expect the music to move to somewhere else.
2nd Inversion – When the 5th of a chord is in the bass, this is called a 2nd inversion. A C chord with an G in the bass is a 2nd inversion chord. C/G
This kind of chord is very unstable. It wants to move. When hear a chord like this we expect the music to go somewhere or to resolve. It feels like we’re hanging on a cliff and we need some resolution!
We could also say that a 2nd inversion chord is like an inverted pyramid. 
Very unstable.
