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Michelle Chan

On hearing the words 'amusement park', the first thing that comes to mind for most of us is the roller coaster.

The train that swoops wildly up and down those steep, sloping tracks is the dominant feature of most amusement parks around the world.

Almost everyone who's been to Ocean Park or Disneyland  has gone on a roller-coaster  ride.

Have you ever wondered how the roller coaster works and how it achieves its high speeds?

The roller coaster is not motor- or engine-driven. Natural laws of physics do all the driving. The only bit of outside help comes from a cable attached to the cars to give the roller coaster its initial lift, up to the top of the first peak or hill.

After that, the laws of physics and acceleration take over. According to these laws, the higher an object goes, the greater its potential or storage energy; when the train ascends, it builds up a supply of potential energy.

This stored energy is then released as kinetic, or moving, energy when the train descends the first downward slope.

It is this burst of energy that takes the train up the second slope or 'hill'. As the train goes up, the kinetic energy is converted back to potential energy.

As the roller coaster goes up and down the 'hills' of the track, its energy keeps shifting back and forth from potential to kinetic.

The higher the level or point the train is descending from, the greater the kinetic energy available to push it up the next hill, and the faster the train

will go. Over the course of the ride, some energy is lost to friction and wind resistance.

You'll notice that towards the end of the ride the loops tend to get smaller, and they are set at a lower height. This is because, by this time, there is less energy overall to propel the roller coaster.

Now you may ask what keeps the roller coaster so firmly attached to its curved path, even when upside down, at the top of a loop.

Let physics explain: When an object moves in a circle, which is what a roller coaster does when it moves through a loop, the moving object is forced inward toward what is called the centre of rotation.

It's this push, known as centripetal force, that keeps  the roller coaster on its curved  path.

This is why your car will not fall off the track even if it's hanging upside down at maximum height.

Roller coasters can be classified according to the material they are made of. Steel roller coasters are characterised by the smoothness of the run, and are extra exciting because of all the loops along the steel track.

Compared with steel, wood is limited as a material, and that's why the tracks of a wooden roller coaster seldom form loops.

Fans of wood roller coasters enjoy the rough feel of a  wood track.

The design of roller coasters has evolved over the years, mainly to heighten the excitement of the ride. In the traditional roller-coaster car,  you sit facing forward.

In some of the new designs, you either stand all the way (suitably strapped, of course), or you sit with your legs dangling in the air.

Some roller coasters are even designed to travel in reverse -  so passengers cannot see what thrill comes next.

There are three big roller coasters in Hong Kong - the Dragon at Ocean Park and the Mine Train and Space Mountain at Disneyland. The Dragon is the only one that offers the upside-down experience.

No matter what type of roller coaster you choose, remember to buckle your seat belt firmly - and never stick your arms out.

Then sit back and enjoy  the ride!

Fun facts

Matterhorn Bobsleds, built in 1959 at Disneyland,  California, was the world's first tubular steel coaster.

The Corkscrew, set up in 1975 in  Buena Park, California, was the first roller coaster with a 360-degree vertical loop.

The Riddler's Revenge, opened in April 1998, is the tallest and fastest stand-up roller coaster in the world. It is located at Six Flags Magic Mountain in California. In an hour about 1,800 people board the coaster for the three-minute ride.



Thrills of a roller coaster