>When I think of acceleration, I think of a gradual speeding up like a car.

This is I think the key point of confusion. Acceleration can happen if very short distances and times, and in fact some of the largest acceleration values happen in extremely short distances and times.

For a basic demonstration, take a penny and hold it a meter over the floor, then let it go. It falls to the floor, and stops. (I'm going to ignore air resistance here)

When you let go, it immediately accelerates downwards at 9.8m/s^(2), or 1G. This continues until it hits the floor. It will be traveling downwards at a speed of about 4.4m/s after traveling one meter.

When it hits the floor, it decelerates, or more accurately, it is accelerating upwards. Now, how much it accelerates is going to depend on what your floor is made of, and how long it takes for it to come to a stop. Lets say in takes 0.1s to come to a stop, from initial contact.

For your penny to go from 4.4m/s to 0m/s in 0.1 second is actually a pretty big acceleration. 44m/s^(2), or about 4.5Gs.

If you somehow had a magic floor that could get that penny to stop in .001s, that penny would experience 450Gs!

Another example of extreme acceleration in a short space and time would be a bullet fired out of a gun. Initially, the bullet has a velocity of zero. When the gun is fired, the bullet experiences a very large acceleration, until it exits the barrel of the gun.

In short, you can get some really big Gs in a small space and time. This ride is moving around in a small space, and you can easily get 1.5gs in that space.