Period

The period of an oscillating phenomenon is the time required for one complete cycle of the oscillation to repeat identically.

Discover FizziQ

How to measure it in class

With FizziQ, students can measure the period of a sound by analyzing the oscillogram displayed on the screen.

Steps:

Open FizziQ and select the Oscillogram tool. Place the smartphone on a table, away from sources of parasitic noise.
Play a note with a tuning fork, a flute, or a pure tone from FizziQ’s sound library. Capture the signal.
On the obtained oscillogram, identify two successive identical peaks and measure the time separating them using the cursors. This duration is the period T.
Calculate the frequency using the formula f = 1/T. Compare with the frequency displayed by FizziQ’s frequency meter to verify measurement consistency.

Scientific activities on this topic

Several experiments easily achievable with a smartphone, tablet, or computer allow measuring the period of an oscillating phenomenon.

1: Pendulum period - Build a device to precisely determine the period of a pendulum: https://www.fizziq.org/en/activities/period-of-a-pendulum/

2: Tuning forks - Study of tuning fork frequencies throughout history: https://www.fizziq.org/en/activities/tuning-forks/

3: Newton’s cradle - Mechanical energy and conservation of energy law for a Newton’s cradle: https://www.fizziq.org/en/activities/newton’s-pendulum/

4: The scale - Study of the relationship between musical notes and frequencies: https://www.fizziq.org/en/activities/the-range/

Learn more

A bit of history

Galileo, while observing the oscillations of a chandelier in the Pisa Cathedral around 1583, discovered that the period of a pendulum does not depend on the amplitude of motion. This property, called isochronism, led to the first pendulum clocks built by Huygens in 1656.

Orders of magnitude

The period of audible sounds varies from 0.05 ms (20,000 Hz, very high-pitched sound) to 50 ms (20 Hz, very low-pitched sound). A heartbeat has a period of approximately 0.8 s. The Earth revolves around the Sun with a period of one year, or approximately 3.15 x 10^7 seconds.

Period and wavelength

Period is related to wavelength by the relationship lambda = v x T, where v is the propagation speed. For sound in air at 20 degrees C (v approximately 343 m/s), an A 440 Hz has a wavelength of 78 cm.

Additional experiments

The experiment Pendulum period allows precisely determining the oscillation period of a pendulum and verifying Galileo’s laws.

Formula

T = 1 / f

Meaning:

T: period (s)

f: frequency (Hz)

For a simple pendulum: T = 2*pi x sqrt(L / g)

L: pendulum length (m)

g: acceleration of gravity (m/s^2)

Application examples

A clock pendulum makes one round trip in a period of exactly 2 seconds
Household electrical current in France oscillates with a period of 20 milliseconds (50 Hz)
The human heartbeat at rest has a period of approximately 0.8 seconds
The A note (440 Hz) of a tuning fork has a period of 2.27 milliseconds
The Earth completes one full rotation in a period of 24 hours

FAQ

Q: What is the relationship between period and frequency? A: Period and frequency are inverses of each other. T = 1/f. If a sound has a frequency of 500 Hz, its period is 1/500 = 0.002 s, or 2 milliseconds.

Q: How to measure the period of a sound on an oscillogram? A: Identify two successive identical points of the signal (for example, two peaks) and read the time separating them on the time axis. This duration is the period.

Q: Does the period of a pendulum depend on its mass? A: No. For a simple pendulum, the period depends only on the length of the string and the acceleration of gravity. This is a result discovered by Galileo.

Q: Why is period useful in music? A: Because period determines frequency, and therefore the pitch of the note. Two instruments playing the same note produce sounds of the same period.

Q: How does FizziQ measure the period? A: FizziQ analyzes the signal captured by the microphone and displays the oscillogram. Students can use cursors to measure the period, or directly read the fundamental frequency calculated by the application.

Frequency - Amplitude - Wavelength - Oscillogram - Pendulum - Sound wave - Hertz