Amusement Park Physics
How do physics laws affect amusement park ride design?
Roller Coaster
For many people, there is only one reason to go to an amusement park: the roller coaster. Some people call it the "scream machine," with good reason. The history of this ride reflects a constant search for greater and more death-defying thrills.
How does a roller coaster work?
What you may not realize as you're cruising down the track at 60 miles an hour is that the coaster has no engine. The car is pulled to the top of the first hill at the beginning of the ride, but after that the coaster must complete the ride on its own. You aren't being propelled around the track by a motor or pulled by a hitch. The conversion of potential energy to kinetic energy is what drives the roller coaster, and all of the kinetic energy you need for the ride is present once the coaster descends the first hill..
Once you're underway, different types of wheels help keep the ride smooth. Running wheels guide the coaster on the track. Friction wheels control lateral motion (movement to either side of the track). A final set of wheels keeps the coaster on the track even if it's inverted. Compressed air brakes stop the car as the ride ends.
Wooden or steel coaster: Does it make a difference?
Roller coasters can be wooden or steel, and can be looping or nonlooping. You'll notice a big difference in the ride depending on the type of material used. In general, wooden coasters are nonlooping. They're also not as tall and not as fast, and they don't feature very steep hills or as long a track as steel ones do. Wooden coasters do offer one advantage over steel coasters, assuming you're looking for palm-sweating thrills: they sway a lot more. Tubular steel coasters allow more looping, higher and steeper hills, greater drops and rolls, and faster speeds.
Carousel
Carousels are not considered "thrill machines" by any stretch of the imagination. Still, carousels are as reliant on the laws of motion as their more exciting cousins, the roller coasters. It's theoretically possible that, allowed to spin out of control, a carousel could gain enough speed so that the riders would be thrown off. Thankfully, runaway carousels are not the least bit common.
Are some horses moving faster than others?
With all of its beauty and seeming simplicity, the carousel is a delicate balance of motion and forces. All of the horses move through one complete circle in the same amount of time. The horses on the outside of the carousel have to cover more distance than the inside horses in the same amount of time. This means the horses on the outside have a faster linear speed than those at the hub.
What if they're galloping?
On some carousels, the horses go up and down in a galloping motion simulating what it might be like to ride a real horse. For these carousels, the ride designer had to approach the problem of movement around the central axis differently. In a normal carousel, each horse maintains a constant acceleration, radius, and tangential speed (speed tangent to the circular path of the carousel). If you add a gallop to some of the horses, you must consider the forces needed to change that horse's position upward or downward as it goes around the track. In designing with these forces in mind, you also need to take into account the mass of the horse and its rider.
Bumper Cars
Newton 's third law of motion comes into play on the bumper cars. This law, the law of interaction, says that if one body exerts a force on a second body, the second body exerts a force equal in magnitude and opposite in direction on the first body. It's the law of action-reaction, and it helps to explain why you feel a jolt when you collide with another bumper car.
How do bumper cars work?
Bumper car rides are designed so that the cars can collide without much danger to the riders. Each car has a large rubber bumper all around it, which prolongs the impact and diffuses the force of the collision.
The bumper cars run on electricity, carried by a pole on the back of the car that leads up to a wire grid in the ride's ceiling. This grid carries the electricity that runs the car. Electrical energy carried to the cars from the grid is converted to kinetic energy, some of which is converted to heat.
What happens to the drivers?
When bumper cars collide, the drivers feel a change in their motion and become aware of their inertia. Though the cars themselves may stop or change direction, the drivers continue in the direction they were moving before the collision. This is why it's important to wear a seat belt while driving a real car, since otherwise you could suffer injury being thrown forward in a collision.
The masses of the drivers also affect the collisions. A difference in mass between two bumper car riders will mean that one rider experiences more change in motion than the other (or more of a jolt). The type of collision, velocity of the cars, and mass of the individual drivers all come into play in bumper car collisions.
Free Fall
Galileo first introduced the concept of free fall. His classic experiments led to the finding that all objects free fall at the same rate, regardless of their mass. According to legend, Galileo dropped balls of different mass from the Leaning Tower of Pisa to help support his ideas.
A freely falling body is an object that is moving under the influence of gravity only. These objects have a downward acceleration toward the center of the earth. Newton later took Galileo's ideas about mechanics and formalized them into his laws of motion.
How do free-fall rides work?
Free-fall rides are really made up of three distinct parts: the ride to the top, the momentary suspension, and the downward plunge. In the first part of the ride, force is applied to the car to lift it to the top of the free-fall tower. The amount of force that must be applied depends on the mass of the car and its passengers. The force is applied by motors, and there is a built-in safety allowance for variations in the mass of the riders.
After a brief period in which the riders are suspended in the air, the car suddenly drops and begins to accelerate toward the ground under the influence of the earth's gravity. The plunge seems dramatic. Just as Galileo and Newton explain in their theories of free fall, the least massive and most massive riders fall to the earth with the same rate of acceleration. If the riders were allowed to hit the earth at that speed, coming to a sudden stop at the end of the ride, there would certainly be serious injuries. Ride designers account for this by building an exit track. The car is attached to this track, which gradually curves toward the ground. A stretch of straight track allows the car to slow down and brake, producing a controlled stop at the bottom, that keeps passengers from getting injured.
Pendulum
Pendulum rides are a little like the swing sets you might remember from your childhood. Swings give you a feeling of flying in a controlled manner. You pump your legs to provide enough force to increase the height of the swing's arc, and enjoy the increased velocity of the downward swing. When you stop pumping, the swing gradually slows and then stops.
What causes the feeling of "weightlessness" on pendulum rides?
Riders often experience near-weightlessness as they approach the top of a pendulum ride. If the ride is the type that makes a complete 360-degree circle, they experience a feeling of complete weightlessness.
Feelings of weightlessness are not due to a decrease in forces of gravitation; people do not feel forces of gravity. What you feel is the force of a seat (or other external object) pushing on your body with a force to counteract gravity's downward pull. A 180-pound person at rest in his office chair experiences the seat pushing upwards on his body with a force of 180 pounds. Yet at the top of a pendulum ride, the same 180-pound person will feel less than this normal sensation of weight. At the very top of the pendulum ride, riders begin to fall out of their seats. Since a 180-pound person is no longer in full contact with his seat, the seat is no longer pushing on him with 180 pounds of force. Thus, the rider has a sensation of weighing less than his normal weight.
Why do riders experience high g-forces on pendulum rides?
As riders pass through the bottom of the circular arc, they often experience high g-forces. Once again, these g-forces are not evidence of increasing forces of gravitation, but the result of increases in the amount of force applied by the seat upon their bodies. Understanding this demands a little information about circular motion.
The motion of an object in a circle requires that there be a force directed toward the center of the circle (sometimes called a "centripetal force"). This means that at the bottom of the circular swing, there must be an upward force (since the circle's center is upward). Gravitational forces are always directed downward upon a rider's body; thus, gravitational forces cannot meet this centripetal force requirement. The seat must supply the centripetal force, pushing upwards on the rider with a force greater than gravity's downward pull. For a 180-pound person, the seat might have to supply 360 pounds of upward pull. This is twice the usual amount experienced by our 180-pound rider. For this reason, we would say the rider experiences 2 g's of force (a seat force that is 2 times the gravity force).
Pendulum
Pendulum rides are a little like the swing sets you might remember from your childhood. Swings give you a feeling of flying in a controlled manner. You pump your legs to provide enough force to increase the height of the swing's arc, and enjoy the increased velocity of the downward swing. When you stop pumping, the swing gradually slows and then stops.
What causes the feeling of "weightlessness" on pendulum rides?
Riders often experience near-weightlessness as they approach the top of a pendulum ride. If the ride is the type that makes a complete 360-degree circle, they experience a feeling of complete weightlessness.
Feelings of weightlessness are not due to a decrease in forces of gravitation; people do not feel forces of gravity. What you feel is the force of a seat (or other external object) pushing on your body with a force to counteract gravity's downward pull. A 180-pound person at rest in his office chair experiences the seat pushing upwards on his body with a force of 180 pounds. Yet at the top of a pendulum ride, the same 180-pound person will feel less than this normal sensation of weight. At the very top of the pendulum ride, riders begin to fall out of their seats. Since a 180-pound person is no longer in full contact with his seat, the seat is no longer pushing on him with 180 pounds of force. Thus, the rider has a sensation of weighing less than his normal weight.
Why do riders experience high g-forces on pendulum rides?
As riders pass through the bottom of the circular arc, they often experience high g-forces. Once again, these g-forces are not evidence of increasing forces of gravitation, but the result of increases in the amount of force applied by the seat upon their bodies. Understanding this demands a little information about circular motion.
The motion of an object in a circle requires that there be a force directed toward the center of the circle (sometimes called a "centripetal force"). This means that at the bottom of the circular swing, there must be an upward force (since the circle's center is upward). Gravitational forces are always directed downward upon a rider's body; thus, gravitational forces cannot meet this centripetal force requirement. The seat must supply the centripetal force, pushing upwards on the rider with a force greater than gravity's downward pull. For a 180-pound person, the seat might have to supply 360 pounds of upward pull. This is twice the usual amount experienced by our 180-pound rider. For this reason, we would say the rider experiences 2 g's of force (a seat force that is 2 times the gravity force).
Ride Safety
Going on amusement park rides is one of the safest forms of recreation. According to the International Association of Amusement Park Attractions, you are more likely to be injured when you play sports, ride a horse, or even ride a bicycle. Statistics show the occurrence of death to be approximately one in 250 million riders.
What do other numbers say?
This group's statistics are supported by those of the National Consumer Product Safety Commission. It estimates that more than 270 million people visit amusement parks each year, and that 7,000 people out of those 270 million go to emergency rooms for injuries they receive on amusement park rides--that's only 0.00259 percent of riders.
What causes injuries?
Both of these groups report that the main reason for deaths and injuries on amusement park rides is preventable error. This would include such things as the lack of routine maintenance and the disregard of safety rules by both operators and riders. Almost every ride has a set of safety rules. These usually require that riders meet certain criteria relating to age, height, and weight, or warn them not to ride if they have certain medical conditions.
For example, small children might be barred from some rides because of their low body mass. People with back or neck problems may be at a greater risk of injury on rides that create force on these areas. A ride's designers understand the forces acting on the rider and create the safety rules for his reason.
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