How do you know a roller coaster is safe?
What makes a roller coaster ride exciting?
Place a marble on a table and turn a round cake pan upside down over it. Move the cake pan around so you can hear the marble rolling around in a circle against the inside edges of the pan. When you have the marble traveling in a consistent circle, pick up the cake pan. Does the marble keep moving in a circle? Why?
Have you ever been on a roller coaster? How did it make you feel? Did you wonder how the car stayed on the track?
What is the highest roller coaster you've ever ridden? How big can a roller coaster be before it is unsafe? How do you think engineers figure out how to make a roller coaster safe?
Isaac Newton never had a chance to ride a roller coaster. The first one was built 75 years after his death. But the principles involved in roller coasters are right up Sir Isaac's alley.
Newton's laws of motion describe how forces determine the motion of objects. Designers rely on the acceleration caused by those forces to make a roller coaster ride both thrilling and safe. The trick is knowing how to use the forces properly. If the forces are too great in one direction, for instance, they'll throw the car off the track. If an upward force is too large (giving you a feeling of heaviness), your heart cannot pump enough blood to your head and you faint. On the other hand, the lack of supporting forces can create feelings of incredible lightness. This can provide an electrifying ride that delivers you safely to the end.
Hypercoasters are about twice as tall as regular roller coasters. This larger scale adds new design challenges. Going down a 200-foot hill, a car has more time to accelerate and gains more speed. If while going at this fast speed the car experiences a sudden change in direction or speed, the car's acceleration changes. A big or sudden change in speed or direction can make a bigger acceleration. Since the force acting on the car (and you) is equal to its mass times its acceleration, the bigger the change in direction or speed and the less time that change takes, the greater the acceleration and the bigger the force you'll feel.
To keep these forces at safe levels, the designer has to stretch out the time and the distance it takes to navigate the curve at the bottom of the hill. This spreads the change out over time, decreasing the force you feel. The top of the next hill has to be high enough to slow the coaster down, or stretched out to a gentler or banked curve, so the car doesn't fly off the track.
Space is a problem. Coasters go forward two feet for every foot they climb. If the highest hill is 100 feet, it takes about 200 horizontal feet to get the car that high. If the highest hill is 200 feet, it takes 400 feet. Since land is expensive, the designers have to be creative about the use of space. A track shaped into a curve takes up less space than one left in a straight line.
Colt, G. & Rentmeester, C. (1993, Aug) The physics of fear. Life, pp. 68-72.
Farrell, K. (1993, Oct 22) Holy Batman, the ride. Science World, p. 19.
Silverstein, H. (1996) Scream machines. Roller Coasters -- Past, present, and future. New York: Walker.
Timney, M.C. (1996, June) Ups and downs of coaster physics. Boys' Life, p. 50.
Zubrowski, B. (1985) Raceways -- Having fun with balls and tracks. New York: William Morrow and Company.
World of coasters:
3M Learning Software: What's the secret? (vol 1). CD-ROM for Macintosh or Windows. (800) 219-9022.
American Coaster Enthusiasts
PO Box 8226
Chicago, IL 60680
The Wildest Ride
Put physics to work by designing the ultimate in scary roller
Roller coaster design is a balance between a wild ride and safety. You try it.
Materials (for each group)
1. Divide into groups.
2. Cut the pipe insulation in half lengthwise to make two long chutes. Using classroom furniture and materials as supports, each group should build a roller coaster. Use tape to hold the coaster in place. Start each ride at 1 meter (3.3') high. Build the wildest ride you can that still delivers the marble to the end. Make the turns and dips as tight as possible. Measure the radius of the turns at the points where they work without a crash.
3. When all coasters are finished, evaluate them. Time five runs on each coaster. Rate each coaster on the following:
4. Test all the coaster tracks using a steel ball instead of a marble. Compare the times of the runs of this ball to the times for the marbles.
5. Work together as a class to design the "ultimate coaster" on the blackboard. Use the best qualities of each group coaster. Build and test your ultimate coaster. Decide what the best qualities for a ride are.
6. Build a hypercoaster. Start the first hill at 2 meters (6.6'). Make each hill twice as high as on your "ultimate coaster." Make the turns as tight as possible. Compare your hypercoaster to your ultimate coaster. Measure the radius of the turns at the point when they work without a crash. How do they compare between the two coasters? Evaluate the hypercoaster using the list of criteria. Would you change the design in any way because of the size?
Hold a marble against the side of a large mixing bowl or wok. If you let it go, will it roll all the way up the other side of the bowl? Will it fly out? Try it. What happened? What is affecting the way the marble behaves? Try it with different-sized marbles or other small balls. Are they any different?
Tie a nut to the end of a string and a toothpick to the string about 10 cm (4") above that. Put the nut and the toothpick in a clear, 2-liter plastic bottle so that the toothpick is horizontal and you can hold the bottle up by the string. Stand on a chair and let go of the string. Where is the nut during the fall? What happens when it hits?
Do this outside on a warm day. Put about 2 liters (1/2 gal) of water in a bucket. Swing it in a circle vertically so it goes from upright to upside down and back again. First try it as fast as you can and then slow down. What happens? Why?
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