Astronaut and wringer
Centripetal acceleration and rotational speed - FizziQ
Author:
Title 4
Learning objectives :
This experiment allows students to understand the concepts of centripetal acceleration and g-force in a concrete way. It establishes a tangible link between theoretical physics and a real application in the space domain.
Concepts covered
Centripetal acceleration, G force and its physiological effects, Uniform circular motion, Relationship between radius, angular velocity and acceleration, Physiology and limits of the human body
What students will do :
The student transforms a salad spinner into a miniature juicer by placing their protected smartphone inside, then measures the maximum centripetal acceleration generated during rotation. By comparing this value to the limits of human tolerance, the student evaluates whether an astronaut could withstand this acceleration. It then calculates the rotational speed in revolutions per minute and analyzes how the size of the basket influences the acceleration.
What is required :
Smartphone with the FizziQ application, Salad spinner, Protection for the smartphone, Stopwatch (optional), Tape measure to measure the radius of the spinner
Scientific background :
Centripetal acceleration is the force that keeps an object on a circular path. It is directed towards the center of the circle and is calculated according to the formula a = v²/r = ω²r, where v is the tangential speed, r the radius of rotation and ω the angular speed. In this experiment, the smartphone's accelerometer measures this acceleration in units of g (1g = 9.81 m/s²). Astronaut training centrifuges use this same principle to simulate the forces supported during takeoff or atmospheric reentry. The physiological effects vary depending on the intensity: at 2-3g, blood accumulates in the legs; at 4-6g, an untrained person may lose consciousness; above 9g, even trained pilots risk blackout. The relationship between radius and centripetal acceleration is particularly important: for the same angular speed, the acceleration increases proportionally to the radius. This is why professional juicers usually have large radii (4-8 meters).