Is the centripetal force a non-contact force
With Isaac Newton on the roller coaster
Anyone who rides a roller coaster can feel how great the forces are that are at work. Because only they make the special thrill of rapid descents and loops possible. They also ensure that the occupants of the last car often enjoy the most “uplifting” roller coaster experience.
A classic roller coaster ride begins with the car being pulled up to the first hill, the lift hill, with the help of a chain drive. From then on he continues his journey independently. Because normally roller coaster trains do not have their own drive (the exception being the rather rare Powered Coasters). The energy that the car has due to its height above the ground is called positional energy or potential energy and this must be sufficient for the entire journey. The energy involved in moving the car, i.e. the kinetic energy, is still very low on the lift hill. But that changes suddenly when the car reaches the first exit. As it races towards the ground, its potential energy is converted into kinetic energy - the car loses height, but increases in speed. The kinetic energy is greatest and the potential energy is lowest in the valley. Then the car drives up the next hill and the form of energy changes from kinetic to potential again.
Wooden roller coaster
This game of transformation continues the whole roller coaster ride, whereby the sum of the two energies always remains constant. If some of the initial energy wasn't converted into heat by friction, the roller coaster ride could last forever.
Gravitation and acceleration in the roller coaster seat
The amusement parks keep setting new speed records, but speed alone says little about driving pleasure. What makes the ride exciting are the accelerations that affect the body. The physicist speaks of acceleration not only when the speed increases, but also when slowing down or changing the direction of movement, i.e. when cornering, hills or valleys. Accelerations are caused by various forces. In a descent, the gravitational force accelerates the car. During the journey, the acceleration of the car can be just as great as the acceleration of a body in free fall towards the center of the earth. In this way the gravitational force is balanced. We cannot feel our own weight and feel weightless for a short time.
If the car drives through a valley or a curve, the direction of movement is guided by the rails on an arcuate path. As a result, the passenger feels a force that pushes him down in the valley or out in the bends. This force is called centrifugal force and is greater the higher the speed and the stronger the curvature. In the basin, centrifugal force and gravity work in the same direction. The passenger feels significantly heavier than usual.
Roller coaster type "Wild Mouse"
If the car drives over the top of a hill, the centrifugal force acts in the opposite direction. If the speed is high enough, the radial acceleration away from the seat, which is caused by the centrifugal force, can even be greater than the acceleration due to gravity. The passenger is lifted in his seat and only held in the car by the bracket. The roller coaster enthusiast speaks of the negative in this caseG or from "Airtime".
Centrifugal forces occur every time you turn a corner. To mitigate their effects, the rails are often inclined so that the passenger is not accelerated to the side but to the floor of the car. The smaller roller coasters of the “Wilde Maus” type, which can often be found at annual fairs, are an exception. They have a large number of very tight curves with no rail inclination. The visitors here have the feeling that the car is in danger of derailing.
Car in the loop
The centrifugal force is also crucial for another spectacular element of a roller coaster: the looping. In a loop, the car goes through a 360-degree loop and is upside down for a short time. Even today there are roller coasters where visitors are only secured by a simple lap bar. This is only possible because the centrifugal force at the highest point of the loop is at least as great as the weight. It then acts like an "artificial gravity" that keeps the passenger in the car.
The right choice of place
With all this knowledge about forms of energy and forces, we can now investigate the explanation of a phenomenon that is observed in many amusement parks: Why are the queues for the first and last seat the longest when the entire train always travels at the same speed? The explanation for the front seats is simple: the passenger feels the wind more strongly and has an unobstructed view of the rails in front of him. For that reason alone, the journey seems faster to him. However, other effects are important for the rear seats.
So far, we have always considered a single car in our considerations, which we assumed to be so small that its size did not matter. On a roller coaster, however, there are very often long trains that consist of several cars. The cars exert additional forces on each other. You can push each other or pull others behind you. Of course, all the wagons in a train have the same speed at all times, since they are firmly connected to one another. The speed that a car has at a certain point on the track can, however, differ from that of another car when it was in the same place.
Choosing a place in the roller coaster
Let's assume that our roller coaster train consists of five cars. He is currently on the lift hill and slowly moves towards the descent due to the slight incline of the rails. The first car drives leisurely over the hilltop. Then the weight of the first car accelerates the entire train. With every car that crosses the hilltop, the effective force increases. When the last car is at the top, the roller coaster train has already reached a high speed. A higher acceleration acts on the passenger of this car than on the occupants of the front car, because the centrifugal acceleration increases with the square of the speed. So he feels the desired airtime on the first and highest descent more intensely than the others.
The entire train continues to increase in speed until the middle car hits the bottom of the valley. At this point, two cars are already on the climb and two are still on the descent. The weight forces of the rear, which accelerate the train, and those of the front, which brake the train, cancel each other out, provided the train is evenly loaded. The middle car travels through the valley at the highest speed, which is why the strongest positive ones have an effect on itG-Forces. Then the train slows down until the middle of the train has passed the next hill and the game starts all over again. The middle cars are slowest on hills and fastest in valleys, so they are less popular with roller coaster riders than the outer cars.
The rule that the ride in the rear car is more exciting than the middle one applies especially to roller coasters with long trains and lots of airtime elements. On routes with many inversions, i.e. overhead elements, other courses could promise more fun. If the cars have more than two seats per row, there are noticeable differences even here. Passengers in the outer seats, for example, drive over longer distances in the same time as those in the center, and are therefore subject to higher accelerations.
How roller coasters slow down - and sometimes take off
After so much classic mechanics, now a little bit more about the modern technology of roller coasters. Roller coaster trains can weigh several tons and reach speeds well over 120 kilometers per hour. Normal brakes, which work according to the principle of friction, are subject to extremely high levels of wear with such requirements. But there are also non-contact braking technologies that work on the principle of electromagnetic induction.
Initially, these eddy current brakes were used in free-fall towers. Here a gondola with the passengers is slowly pulled to a great height. Once at the top, it is released and then falls down completely freely. Strong permanent magnets are attached to the nacelle, and brake blades made of conductive material are located in the lower area of the tower. When the nacelle comes into this area, the magnets induce eddy currents in the conductors. These currents again form a magnetic field that is opposite to the causal magnetic field (Lenz's rule of induction). The gondola is slowed down as a result. The faster the conductor and magnetic field move against each other, the stronger the braking force.
A vital benefit of these brakes is that they work perfectly even in the event of a power failure. Eddy current brakes have also been used on roller coasters since the 1990s. The magnets are usually on the rail and the brake blades on the car. However, normal friction brakes are still essential, because the magnetic brakes only work when there is a relative movement between the magnet and the conductor, i.e. they cannot bring the train to a complete standstill or hold it on an incline.
Fastest roller coaster in the world
Lenz's induction rule is also used in modern drive systems. In addition to the chain elevator, there is the possibility of giving the train enough energy for the journey with a catapult launch. This type of track has been used since the mid-1990s and the introduction of the LIM (linear induction motor) in roller coaster construction. The roller coaster car can be accelerated almost from a standing position on a horizontal track. The principle of the LIM follows that of an AC motor, only that a linear instead of a rotating movement is generated here.
In simplified terms, coils are attached to the rails to which alternating current is applied. This creates a wave-like “traveling field” that moves along the rails. Ladder swords are attached to the roller coaster cars, in which the magnetic field induces eddy currents. An opposing field is created. The repulsive effect of both magnetic fields is used in such a way that the magnetic field of the car is practically pulled behind by the traveling field. In order for this to work at all, complex electrical control technology and position measurement of the car with millimeter precision are required. In addition, enormous amounts of energy are required for a short time, which can put the power grid of an amusement park to the test. So there are many challenges to overcome, but the feeling of driving when a car weighing tons is accelerated to around a hundred kilometers per hour in a few seconds is worth the effort for many amusement parks.
However, speed records cannot be achieved with this system. This would require very high amounts of energy to be made available in a very short time, which the park's power supply would not be able to cope with. The currently fastest roller coaster in the world, the “Formula Rossa” in Dubai, accelerates to 240 kilometers per hour in 4.9 seconds. A hydraulic drive is responsible for this, in which the amount of energy is compressed over a longer period of time and then suddenly released at the start.
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