![Amazing Mirror & Air Experiment](https://hight3ch.com/wp-content/uploads/2016/08/amazing-mirror-air-experiment.jpg)
This is a demonstration of the Schlieren effect. This setup allows you to see changes in air density. The point light source is aimed at the concave mirror. The concave mirror reflects to a focal point. There you use a sharp edged object to partially block the light which helps create a shadow effect that allows you to see air movement.