Denna sida på svenska This page in English

Gondola motion

The photo sequence above shows the star of Mechanica approaching the ground. The photos are collected from a video, with intervals of 0.4s. The dot marks one of the gondolas approaching the ground, showing how the changed orientation leads to a rotation around the gondola axis. (Full-size photo)

The graph to the right shows the accelerometer data for the "longitudinal" component (green) of a rider in Mechanica together with the total "G force". The graph around 40 seconds shows the result when the star is close to the bottom and the rider experiences just over 2G. The data after 60 seconds shows a few of the damped oscillations at the top.

A negative value for the longitudinal component corresponds to facing down. At the top, the oscillations go between nearly ±1G, corresponding to swinging between ±90° - facing straight up or straight down. The period of rotation 2s. corresponds to that of a mathematical pendulum of about 1m. It is worth noting that - unlike an ordinary playground swing, the total G force does not increase significantly while passing the lowest point. This can be attributed to the location of the accelerometer sensor, close to the axis of gondola rotation. 

For the star in the lowest position, the amplitude is larger and the longitudinal component changes slightly more than between ±2G although the angle still moves between ±90°. The larger amplitude is due to the centripetal acceleration related to the main rotation.

This G factor is analogous to a higher value of the acceleration of gravity as the star passes the lowest point. For stronger gravity, the period becomes shorter, by the square root of 2, and, indeed, the time required to swing from face down to face up is only about 0.7s, as seen from the accelerometer graph. This time was also measured from the video clip used to obtain the photo sequence below. The photos below start 1.0s after the sequence on the top of the page, and with the same interval, 0.4s. Here also the direction of the back seat of the gondola has been indicated. (Full-size photo.)