A quick and very accessible method for the measurement of acceleration due to gravity is presented. The experimental setup employs a smartphone ambient light sensor as the motion timer for measuring the period of a simple pendulum. This allowed us to obtain an experimental value, 9.72 + 0.05 m s −2 , for the gravitational acceleration which is in good agreement with the local theoretical value of 9.78 m s −2 .

An accessible smartphone-based experimental set-up for measuring a spring constant is presented. Using the smartphone ambient light sensor as the motion timer that allows for the measurement of the period of oscillations of a vertical spring-mass oscillator we found the spring constant to be 27.3 ± 0.2 N m −1 . This measurement is in a satisfactory agreement with another experimental value, 26.7 ± 0.1 N m −1 , obtained via the traditional static method.

The angular velocity of a spinning object is, by standard, measured using a device called a tachometer. However, by directly using it in a classroom setting, the activity is likely to appear as less instructive and less engaging. Indeed, some alternative classroom-suitable methods for measuring angular velocity have been presented. In this paper, we present a further alternative that is smartphone-based, making use of the real-time magnetic field (simply called B-field in what follows) data gathering capability of the B-field sensor of the smartphone device as the timer for measuring average rotational period and average angular velocity. The in-built B-field sensor in smartphones has already found a number of uses in undergraduate experimental physics. For instance, in elementary electrodynamics, it has been used to explore the well-known Bio-Savart law and in a measurement of the permeability of air.

The internal sensors in smartphones for their advanced add-in functions have also paved the way for these gadgets becoming multifunctional tools in elementary experimental physics. For instance, the acceleration sensor has been used to analyze free-falling motion and to study the oscillations of a spring-mass system. The ambient light sensor on the other hand has been proven to be a capable tool in studying an astronomical phenomenon as well as in measuring speed and acceleration. In this paper we present an accurate, convenient, and engaging use of the smartphone magnetic field sensor to measure the acceleration due to gravity via measurement of the period of oscillations (simply called “period” in what follows) of a simple pendulum. Measurement of the gravitational acceleration via the simple pendulum is a standard elementary physics laboratory activity, but the employment of the magnetic field sensor of a smartphone device in measuring the period is quite new and the use of it is seen as fascinating among students. The setup and procedure are rather simple and can easily be replicated as a classroom demonstration or as a regular laboratory activity.

Mainly, a door alarm system is used to measure gravitational acceleration. The magnetic switch component of the door alarm is turned on or off as the magnetic pendulum bob approaches or recedes from it. The audio signals is recorded by a smartphone as a time series, permitting the measurement of the period of oscillations and thus the determination of the gravitational acceleration. A satisfactory match between the experimental and the locally accepted value is attained. The setup is also an apparent audio-based demonstration of the periodicity of the motion of the simple pendulum.