Can't We Store Mechanical Energy

A flywheel is a rotating mechanical device that is used to store rotational energy.

Consider also the Weight-driven clock.

Don't forget wind up toys and things like that.

Indeed, the Spring-driven clock.

In addition to the excellent examples in answer #1, you can also consider things like:

Pumped Hydro

Various types Hydraulic accumulators

Compressed air

To the list add:

Torsion;

Tension;

Pendulum;

For centuries before we harnessed electricity, humans have been storing mechanical energy in all kinds of ways, it was all they had.

One could even argue that electricity has made us lazy...

To quote comedian George Goebel,

"Before they had the electric light, we all had to watch TV in the dark!"

Many years ago the British (national) coal board (NCB) tried flywheel powered tow trucks for underground haulage in deep gaseous mines. The flywheel and DC motor/generator were in a hydrogen atmosphere to reduce friction. (It doesn't sound good so far). Apparently they were quite good, BUT heavy on maintenance. So another British idea hit the accountancy wall!

Yep. Whatever it is, push it up to the top of the hill.

Some public buses in switzerland hav a huge flywheel under the floor to get the energy for starting and short uphills.

More sophisticated flywheels are used (or considered to) in the middle of railway tunnels to feed the line when train passes and avoid voltage drop when the train is in the middle..

There is a company near me that developed a flywheel based car, got upwards of 100mpg if I recall correctly. But they were having trouble getting venture capital to move ahead, people don't like new ideas if they don't involve bit twiddling now.

Found it: http://en.wikipedia.org/wiki/AFS_Trinity

This is a bit of heavy reading http://www.dmm-pitwork.org.uk/html/brookhouse.htm

A Ward Leonard system with a flywheel to take up peaks in load for a mine winder.

Try to abuse any thugs, you can store some mechanical energy on face for some time.