Wuhan Hotel has a projection.

The rough surface of the screen is used to diffuse light so that all students can see the patterns on the screen;

The projector is made by using the principle of magnifying the real image upside down when the object distance is between the focal length and the double focal length.

Installing wheels on the base can change sliding into rolling, which can reduce friction.

So the answer is: rough; True; ? Reduce friction.