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Q & A: Tennis Ball Roller Coaster!

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Q:
How would you build a roller coaster that would use tennis balls as passengers. We have to have a jump, a corkscrew and a loop-d-loop incorporated into our design. We need to utilize gravity and have the balls go as fast as possible through the course. Can you give us some ideas?
- Anonymous (age 8)
Chippewa, Brecksville, OH, Cuyahoga
A:
Cool project! I actually did one of these a number of years ago from a kit. Mine used small metal balls instead of tennnis balls, but the basic ideas are the same. What I used was a flat base that I could attach a whole bunch of tall metal rods to. The metal rods stood straight up and held up the tracks every ten inches or so, which were made out of two long plastic cords. (Since you're using a bigger ball, you probably can get away with attaching something to the track only every 15 or 20 inches.) The cords were separated so that the balls could roll on them. If you decide to use this basic plan, you'll have to figure out a way to attach the cords to the metal rods, since you probably won't be able to find the same type of connectors that I used.

The most important thing to remember when building your roller coaster is that the ball would always prefer to go in a straight line. For example, this means that when you build the jump, the part of the track that the ball lands on has to be lined up straight with the part of the track that it jumped off of.

This will also make it harder to have the ball turn corners. When you build a corner into the track, it's important that you have it be "banked." Banking the corners means that the track tilts inward around the curve. (If you've ever seen one of the tracks that they use for racing cars, you should know what this looks like.) This helps to keep the ball from rolling in a straight line right off the track. This will probably be important to remember when you're building your corkscrew.

Also, the ball would prefer to be going downwards. In order to have it do anything where it has to move upwards, you have to make sure that it's going very fast first. This means that it has to roll down a hill before it will be able to roll up one. (And because it loses some energy by rolling, the hill it rolls down should be taller than the one it has to roll up.) The ball's energy comes from how high up it starts, and gravity pulling it towards the ground is what keeps it going and speeds it up. So, unless you can use an electric elevator of some sort, you will probably have to have your track be pretty tall.

The hardest part of all this will be the Loop-D-Loop. The track that I built had one, and it took me a /very/ long time to get this to work. But be patient! It is possible, I promise! Again, remember that the ball will always try to move in a straight line. Unfortunately, Loop-D-Loops require that the ball shift over to the side a bit (because it would be hard for the track to go through itself). The biggest problem you will probably have is that the ball will fall off the track and go to one side or the other. Just keep tweaking the track so that there's always some track in between the ball and where it's heading.

The other tough thing about Loop-D-Loops is that the ball has to be moved up, against gravity. This means that the ball has to be going very fast when it starts it. You can make sure this happens by making a tall hill in the track right before the Loop-D-Loop. Rolling down this will give the ball a lot of speed. Once you get the Loop-D-Loop to the point where the ball doesn't fall off to one side, it will probably just fall straight down from the top of the loop. If this happens, it means that the ball isn't going fast enough. So make the hill before it even taller.

Most importantly, be patient. I would be very surprised if your track works perfectly the first time. Just keep adjusting it until it does work. If there's a problem spot, you can run the ball through it over and over again until you've figured out how to fix it. Good luck!

-Tamara

(republished on 07/19/06)

Follow-Up #1: Roller Coaster Kits

Q:
Tamara, in the tennis ball enginering page, u talk about that rollercoaster with small metal balls. do u remember what the brand name of it was?
- bryan
A:
Bryan -

The kit that I had was the Spacewarp coaster kit made by a company called Bandai. I know that they don't make the Spacewarp kit anymore, but they may have other coaster kits. There's also a coaster kit made by K'nex that is supposed to be pretty good - and it would probably be a lot easier to find.

-Tamara

(republished on 07/19/06)

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