Laser beam in a stream of water

Shine a laser beam through a stream of water, and it will follow the curve of the water flow as it reflects inside the stream.
Science content
Physics: Light and Sound (1)
Lessons activity is in
  • empty water bottle, with a small hole punched lower than midway down
  • pocket laser
  • dark room

Fill the bottle with water, with a finger over the hole, and hold it over a sink.
Let the water stream out of the hole. Ask a student to shine the laser through the bottle and into the start of the stream.
The laser light will be reflected from the sides of the inside of the stream, so it stays inside the stream of water even as it curves, so lighting up the water stream. There is a point where the stream curves too steeply for the internal reflection to continue.

Grades taught
Gr 4
Gr 5