>> I call them fear machines.

My name is Chris Gray.

I'm a mechanical engineer.

I work at Great Coasters International in Sunbury, Pennsylvania.

We design and build wooden roller coasters all over the world.

And I have rollercoaster stuff everywhere.

I made a decision when I was eight years old, this is what I want to do-- trying to figure out what the forces were that would scare someone to make them scream at a particular point of a ride.

A rollercoaster is based all on gravity.

We're building potential energy as we go up the lift.

The higher we go, the more potential energy we have.

So you have to take all those forces and mix it up a little bit to give everything just a little twist of excitement so the person that's actually riding the ride never knows what to expect next.

This is a little miniature rollercoaster.

This is how I got my start in the amusement business, was building these architectural models.

And it was one of the things that I loved to do as a kid.

And I think that's where the dream and the love of doing what