Very good episode Karen.
One small nit, when you talked about the piezo electric sensor you said the crystal was full of ions. That is not correct.
The crystal material is atoms in a lattice which are sensitive to displacement. When you apply a force, the atoms are compressed, which causes them to emit photons, some say electrons but that is another discussion, which carry a charge to a voltage sensor, which then detects the increase in charge flow, which is then converted to the g force amount.
Also, the accelerometer is more of an impulse device. It detects changes, not steady forces, which is why it normally reads zero under the influence of gravity.
I know some people have been confused thinking that the gravitational force should tell them when a device is falling, but under those conditions, the actual force is constant and the device reads zero until it stops moving.
When you combine the three different sensors in a nine dimensional sensor, then you can build up an inertial measurement unit, which can be used to keep track of changes in all three axis during movement.