Does a human slingshot-or ejector seat-ride work on the same science principles as a bungee jump? Why do rides like that make a person feel a little queasy?

SuChin is propelled 150 feet into the air-all in the name of science.
Segment length: 6:15

Insights

Life is full of ups and downs. Sometimes, though, moving between these extremes can be quite entertaining. Just check out the human slingshot-or ejector seat-ride.

The ejector seat ride has its roots in bungee jumping. Both depend on the elasticity of bungee cords to provide a force. In bungee jumping, the elastic force is used to negatively accelerate (decelerate) and halt a jumper's body as it plummets toward the ground. The ejector seat works in reverse. Elasticity overcomes gravity by yanking upward and positively accelerating (propelling) the riders sky-high.

Riders are strapped into a cage that has been pulled down to the ground, stretching the bungee cords connected high above to maximize potential energy. Then the entire unit is released skyward, converting the potential energy of the bungee cords into the kinetic energy of the riders, shooting them 45 meters (150 feet) into the air. At the moment of release, the rider feels the maximum acceleration. Of course, energy is dissipated with each pass as heat is generated by friction between the bungee cords and air and within the cords themselves.

The g-forces caused by the bungee acceleration are the very same forces that affect race car drivers and astronauts. Even when we're just standing around, our bodies experience the force of 1g, as gravity pulls our bodies toward the center of Earth. On the ejector seat, force due to the ride alone may be up to 2g, but the force your body feels is actually 3g, once you add in gravity as well.

The sudden shifting of your body's position upsets the fluid in your inner ear, affecting your sense of balance and triggering responses such as an increased heart rate and tightening of your stomach muscles. Your body seems incredibly heavy as g-forces push you and the blood in your body back in the direction you started from. Your heart works harder to get the oxygen- and nutrient-bearing blood back to the brain and overworked stomach muscles. This creates a temporary chemical imbalance resulting in faintness or queasiness.

At the moment acceleration stops and the bungee cords stop pulling on you, the only force from then on is gravity-you actually experience free fall. Somehow, your body adapts and often you even enjoy the experience.

Connections
1. On the ejector seat, when gravity cancels out upward motion, the rider returns in a brief free fall and is actually weightless. On what other rides would you experience this?
2. In what ways do you experience g-forces in your everyday life? (Hint: G-forces only occur during acceleration-a change in speed.)

Key Words

acceleration change in the speed or direction of motion
bungee jumping sport where a person jumps, while attached to elastic cords, off of a high platform
dissipated released, dispersed
elasticity property of a material to stretch beyond its original shape, as well as to return to its original shape, with varying degrees of strength depending on the material
force of gravity how much the acceleration of gravity makes you weigh against the floor or a scale
force push or pull exerted on or by an object
g-force force exerted by gravity on an object near Earth's surface
kinetic energy energy of a moving body
potential energy amount of energy a body has stored, ready to be converted into kinetic energy
trajectory path a launched object takes through the air
zenith the highest point in the trajectory of a launched object

Resources

1. Breckenridge, J. (1993) Simple physics experiments with everyday materials. New York: Sterling Publishing.
2. Chaos for fun and profit. (1994, Feb 26) Science News, p. 143.
3. Epstein, L.C. (1994) Thinking physics is Gedanken physics. San Francisco: Insight Press.
4. Frase, N. (1992) Bungee jumping for fun and profit. Merrillville, IN: ICS Books.
5. Freeman, I.M. & Durden, W.J. (1990) Physics made simple. New York: Doubleday.
6. Gardner, R. (1990) Famous experiments you can do. New York: Franklin Watts.
7. Pearce, F. (1992, Aug 29) Licensed to thrill. New Scientist, p. 23.
8. Wellnitz, W.R. (1993) Be a kid physicist. Blue Ridge Summit, PA: Tab Books.
9. Whitelaw, I. (1992) Eyewitness science: Force and motion. New York: Dorling Kindersley.

Additional resources

1. 3M Learning Software: What's the secret? CD-ROMs for Macintosh or Windows. (800) 219-9022.
2. NEWTON'S APPLE Multimedia Collection: Physical Sciences (roller coasters). Videodisc and software for Macintosh and Windows. National Geographic: (800) 368-2728.

Main Activity

In the name of science, and for you to completely understand the difference between positive and negative g-forces, Newton's Apple respectfully requests that you make a sacrifice to collect data for this very important experiment. Unfortunately, you'll have to do it at an amusement park.

Materials

• amusement park with a roller coaster
  
• paper
  
• regular and colored pencils
  
• calculator

1. First, go for a couple of rides. Pay attention to when you feel heavy and when you feel light, when you feel your body pressed hard against the seat, and when you feel disoriented or dizzy.
2. Next, sit where you can watch the roller coaster go through its ride. Sketch out as best you can a side view and an overhead view.
3. On your overhead view, color in red the parts of the ride where you felt heavy, coloring darker and heavier at the most forceful parts. This is where you were experiencing positive g-forces.
4. Color in blue the parts of the ride where you felt light, as if the restraining bar on your car was the only thing keeping you from flying out of your seat. This is where you were experiencing negative g-forces.
5. How does this color map compare to your side view? Do positive and negative g-forces correlate with altitude? Do they seem to be associated with certain parts of a turn or an incline or descent? Now mark some dizzy or disoriented spots on your color map. Are they associated with the positive or with the negative g-force experiences?
6. Extra credit: If you hold a penny in the flat palm of your hand (facing toward what is originally upward) throughout the entire ride, it never falls out. Why? Is this due to g-forces or others?

Why do you suppose "ride films" (where people are enclosed in a movie-watching environment to simulate roller coasters or outer space rides) can make you as nauseous as the real thing? Which of your senses are fooled, and which are not? (Check out Simulator Rides, Show 1307, in this packet for more information.)

Both bungee jumping and the ejector seat ride depend on the elasticity in bungee cords to exert forces, whether stopping a falling jumper or launching a human slingshot. Put on some eye protection and gather up a ruler and rubber bands of different sizes and lengths. Using the ruler as a launcher, shoot the rubber bands into an open area where there is no danger of hitting anyone. Do wide bands travel farther than thin bands of the same circumference? Why? How does the traveling distance of the rubber bands change as you pull back on the ruler to different measurements? Why?

Is there any way you can change your apparent weight, as measured on a bathroom scale, while riding a fast elevator in a tall building? Try to determine the positive and negative accelerations of the elevator by watching the readings as you stand on the scale.

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.