Period of a pendulum
Practical Activity for 16-19
In this activity students use the phyphox app to determine the gravitational field strength using a pendulum.
Each student will need:
- A phone with phyphox installed
- A length of string
- A small clear plastic bag which can be sealed (optional)
- Open the phyphox app and click on Pendulum.
- Click on the top right part of the screen and switch on do a timed run (use the default settings of 3 seconds for start delay and 10 seconds for experimental duration).
- Securely attach the phone to one end of the string. For example, you could put it in a clear plastic bag and then attach the string.
- Hold the other end of the string and pull the phone-pendulum to one side. Press play and let the pendulum go.
- Keeping your hand steady, let the phone swing for more than 13 seconds to enable the app to record for at least 10 seconds. Make a note of the period from the reading.
- Measure the length of the pendulum l (length of string + distance to centre of phone).
- Repeat steps 4 to 6 for more pendulum lengths.
- Plot a straight-line graph to determine the acceleration of free-fall g.
If students are unfamiliar with the relationship for the period T of a pendulum introduce it:
T = 2π l g
They can determine g by plotting T 2 against l (the gradient of the straight-line graph will be equal to 4π 2/g).
Students describe an experiment to determine gravitational field strength.