MEMS accelerometers. You can get a 9-axis sensor from the likes of Bosch or Invensys for not a lot of money. 3 accelerations, 3 rotations (gyros), 3 magnetic. Most smartphones have them now.

It is just an etching and plating process within a semiconductor. Say after laying down a plated layer of metal track with a lump on the end (for weight) they then etch away the support having used material that can be etched without eating the metal. So it end up with a bit of metal sticking out in mid air. This is on a microscopic level. It will vibrate up and down when the support is moved.
They have also built in to the semiconductor a strain gauge on the support so it can detect the vibration movement. Build lots of them in different directions during the chip fabrication process.

To make a gyroscope I think they make a u-shaped cantilever that is "released" from the substrate and made to vibrate up and down. Rotation around an appropriate axis causes it also to twist which can be detected separately.

You can easily get hold of one to play with, for instance many of the introductory kits available for the Arduino include one, along with temperature sensors and other fun devices to play with. No soldering required you just hook the devices up with a breadboard. Some of the chips include a magnetic compass as well.

John

That sounds like a particularly complicated way to pick up pendulum motion