The stroboscopic effect occurs when a moving object is periodically illuminated (like with a strobe light) at regular intervals. Our eyes only see the the object at discrete moments, instead of continuously. This causes the motion of the object to appear much different than it normally would -- if you've ever used a strobe light, you know what this looks like. This is called aliasing and it's is what makes the helicopter's blades in the video below look like they aren't rotating -- the frequency of the camera is synced to the frequency of the blades' rotation, so we are only seeing the precise snapshots of the helicopter when its blades are in the exact same position during their rotation, giving the appearance that they are stationary.
For our demo, we match the frequency of the strobe light to the frequency of the mechanical oscillator, and observe the same aliasing effect. This will make the spirals of water look like they are frozen in time or moving very slowly forward or backward, depending on the frequency.
Mechanical Oscillator, function generator, strobe light, funnel, A-stand, rod, tape, pitcher of water, 2 banana cables
- Frequencies close to 60 Hz work well (when using the lowest flashes per minute setting)
- Tape the hose close to it's end to keep water from squirting erratically