Figure 1. Examples of measuring equipment that can be taken along in many different rides
Ann-Marie Pendrill1,2, Sara Bagge1 and Roger Andersson3,4,
Ann-Marie.Pendrill@fy.chalmers.se
- Physics and Engineering Physics, Göteborg University and Chalmers University of Technology, SE-412 96 Göteborg, Sweden
- Noveum, Högskolan i Skövde, Högskolevägen, Box 408, SE-541 28 Skövde, Sweden
- Västerhöjdsgymnasiet, Gymnasiegatan 1, SE 541 31 Skövde, Sweden
- Institutionen för pedagogik, Högskolan i Borås, SE-501 90 Borås, Sweden
Abstract
An amusement park is a large hands-on physics laboratory, full of acceleration and rotation, free-falling bodies and vector additions. Newton's laws are experienced with eyes, hands and body. As a complement to electronic equipment for measurements of acceleration and pulse, simple toys can be taken along on the rides and used to illustrate and measure the forces felt by the body. The investigations also provide models of classical physics experiments. Many of the experiments can also be adapted to the local playground.
Even the uniform, rectilinear motion of Newton's first law can be exciting in the park and also provoke discussions. During the slow haul up in a roller-coaster, the leaning seat may be interpreted by the body as feeling heavier due to acceleration. (The phenomenon is of course used in simulator rides.) Analysis of the motion indicates absense of acceleration, and thus the body experiences only the ordinary weight. Nevertheless, the primary excitement in the park is related to Newton's second law and in the accelerations that follows after the roller-coaster has reached the top, the connection between force and acceleration becomes obvious to the whole body. The relation can also be enhanced visually by simple measuring devices, such as a cuddly animal on a string or a slinky, for measuring horizontal and vertical acceleration, respectively.
Several parks in the US have a long tradition of arranging "Physics Days", in particular for high-school students, who bring their CBLs, data loggers or other devices for measuring acceleration, as described e.g. by Bakken /1/, who also provides ample material for preparing a visit. In this paper we focus on simple experiments that illustrate important principles and can be performed also by younger children. We have found these experiments to be rewarding for children as young as 8 providing the class has prepared the visit and that the visit is integrated with work in school. We also present a few examples of classroom activities for older students that can be used independent of a visit to a park.
Figure 1. Examples of measuring equipment that can be taken along in many different rides
Even if the amusement park is a controlled environment, Newton's laws are still valid. The park maintains the responsibility to protect the visitors also from their own activities, including experiments. The high speeds, strong forces, large energies and high elevations involved lead to special demands on the equipment used. The general rule in rides is "no loose objects" and electronic devices must always be securely attached to the body. The park may be prepared to accept a handheld objects if they are small, lightweight and soft. We discuss in this paper measurements using simple equipment. Some examples are shown in Figure 1. Reliable measurements are sometimes difficult in the fast rides. Nevertheless, the simple devices have the advantage of providing a direct link between the visual observation, the different parts of the ride, and the experience of the body. They can also illustrate important principles that are sometimes obscured by numbers.
Figure 2: A spiral toy used as accelerometer in the "Frog hopper". The spiral works as a built-in dynamometer for the head of the rabbit. When is the spiral short, when is it long and when is it normal length? When do you feel light, when do you feel heavy? On the way up or down, at the top or at the bottom?
Slightly older children may use the larger drop tower rides. Newton's first law obviously applies during the wait for the ascent e.g. to the "Turbo Drop"/4/ tower. It also applies soon after start during the slow ascent, even when you are high up, looking up and find that you still have a long way to go. Newton's first law applies when you wait for several seconds at the top and enjoy the view while waiting for the 2g acceleration from the top. To study if the claims of 2g - twice as fast as free fall - is correct, a plastic mug with about 0.5 cm of water can be taken along /5/. The result is a clear illustration of inertia. The water, exposed only to the gravitational force, cannot fall faster than g and cannot follow the mug. To the rider falling at 2g, it looks as if the water falls normally with 1g - but upwards, as gravity has been turned around. (Don't hold the mug under your chin and don't choose a seat with headwind.) In free-fall rides, such as the "Space shot" /4/, the water instead falls together with the rider, illustrating weightlessness, both to the rider and to observers on the ground. We have found this experiment to be sufficiently visual and easy to be rewarding also for unprepared classes. The observations can be used as a starting point to discuss why astronauts are weightless, in spite of the fact that both the space shuttle and the astronauts are very much affected by gravity, causing them to orbit the earth.
The circular motion of a classical merry-go-round also involves horizontal acceleration, which is, however, orthogonal to the motion and results only in a changed direction of motion, not in increased speed. For a slow carousel, this centripetal force is usually too small to provide a visual effect. As discussed in earlier work /6/ slowly rotating coordinate systems can instead be used to study the Coriolis force, using a cuddly toy on a string to peform a miniature version of the Foucault pendulum experiment, which demonstrated the rotation of the earth. What happens to the swinging toy as the carousel starts?
"In the Pony Carousel, the cuddly toys on the strings started to move like this. I think it was to prove that the Earth is rotating."The quotes are from interviews with 10-year olds three months after a supervised visit as discussed in more detail in previous work /6/."I learned that when going in the Pony Carousel, the cuddly toy kept going in the same direction while I was going around."
Many rides combine different motions. One example is the Mad Tea Party (or "Coffee Cups") ride where the slower rotation of a large circle is superimposed with a faster counter-rotation with a smaller radius. The acceleration in this ride is still purely horizontal and even 5-year old children have been found to enjoy observing the acceleration using a cuddly animal on a string, noting how the angle varies during the ride. Older children may add a protractor to measure maximum and minimum angle and acceleration. The observers on the ground can follow the path of an invividual rider. Giving a selected child a colorful hat or rabbit ears facilitates the observation.
The starshaped path of the rider, resulting from the superimposed motions, depends on the relation between rotational periods and radii of the circles, and can be analysed e.g. with spreadsheet programs or Matlab. When is the speed largest/smallest? When is the acceleration largest? Is the acceleration zero during any part of the motion? What shapes are possible? This type of ride can lead to animated discussion in the classroom - even if no visit is planned. In the next section we discuss other types of classroom activities related to amusement park rides.
Fig. 3: What can you tell about the forces and motion on the rider by looking at the picture?
Roller coasters are prime examples of energy conservation. The conversion back and forth between potential and kinetic energy gives the rapid variation in speed. Using the elevation differences to estimate the speed is a good approximation - as illustrated e.g. by observing the motion of the looping roller coaster "HangOver" in Fig. 4. The train reaches nearly its original height before being hauled up ready for the reverse tour. Looping roller coasters are also textbook examples of centripetal force. How high above the loop would the ride have to start if the riders should be weightless on top? The photo in Figure 4 shows that the bottom of the loop has a significantly larger radius than the top. By analysing the forces in a circular loop, the reason should become evident. The information that the distance between to consequtive wagons is about 2.5 m can be used to estimate the radius of the half-circle at the top of the loop in the picture.
Figure 4. Why does the radius of curvature differ between the top and the bottom of the loop?
Simple rides are often the most rewarding, giving the children time to observe and reflect. Even young children can learn a lot during a visit to an amusement park. The older children can spend more time on quantitative measurement and analysis during the follow-up work. The park can thus be used by pupils of all ages, but the design of the visit must be adapted to the age.
For teachers, the visit may provide a welcome break and a chance to meet colleagues, both from their own school and from other schools. It gives a chance to interact with pupils in a positive environment and to discuss the experiences before and after - and even during - the ride. These are excellent opportunities for "just-in-time teaching" of physics.