Slow motion imaging using your smartphone
In this session, we will use slow motion camera to capture and visualise the vibrations of a string or flexible object.
This page will give you some useful information about how the lab works, and what you will need to complete it.
You will need
Smartphone
The smartphone should be capable of imaging in slow-motion. Usually this option is available in camera settings.
Another person (optional)
It might be useful to have another person to record while you hold the objects
And one of the following:
Guitar / Ukulele
Flexible ruler
Lamp
Slow motion imaging using your smartphone
To capture the video:
Open the camera on the phone and search for the slow-mo (slow-motion) option.
Place the camera so that it faces the object or lamp.
Take a video in the slow-motion setting.
When you watch the video back you can see vibrations or flickering that you would normally not be able to see clearly, because they happen too fast for our eyes to see them clearly.
If using a lamp
In this version of the experiment, you will use a lamp, instead of a flexible object.
Filming this with a slow-motion camera will capture the very fast flickering of the lightbulb that is invisible to our eyes.
The flickering derives from the very fast fluctuation of the current that comes through the mains power supply of your house. This fluctuation is called alternating current or AC current.
If you are using a guitar / ukulele
If using a guitar or ukulele, then gently pluck one of the strings. If you film this in slow-motion you can capture its vibrations
If using a ruler
If using a ruler, place it on a desk so that a third of it is on the desk and the other two thirds hanging free, beyond the desk. Place something heavy on the end that is on the table or hold it. Then, gently push downwards on the end of the ruler that is hanging above the floor. If it is flexible enough, it should move up and down slightly a few times. If it is not so flexible, then try pushing slightly harder.
You will try to capture this motion of the ruler with the camera in the slow-motion setting.
About
Slow motion cameras can be used to show motions in more detail and slowed down. This technique can also be used to change the perception of time in e.g., films.
Our eyes and brains cannot process motions that happen too fast. When you watch a video or a film, you are really watching a series of images that are presented in rapid succession to give the illusion of movement. Modern cameras can take many pictures per second (which is called “frame rate”), more than what is needed to create the illusion of movement.
When you play a video back that was taken in slow motion, your phone is showing you images more slowly than they were originally captured. This means that it takes longer to show all the frames that were taken with the camera. This has the effect of showing motions in more detail than we can normally see.
For example, a camera can capture images at a frame rate of 60 frames per second, and then play them at a 24 frame per second rate. Thus, for every second that you record at 60 frames per second, you can play back 2.5 seconds in slow motion.
