A prism is a transparent object that separates light into individual beams. When light passes through a prism, it forms a rainbow. This is because the prism breaks white light and refracts it separately to form the colors of the rainbow. Make a simple prism with a glass of water and simple household materials.
Fill a clear glass with water, about halfway.
Place the half-filled water glass on an elevated surface, such as a window sill or a coffee table, so half the glass sits on the surface and the other half overlaps the edge of the surface. Be careful when positioning the glass, so it does not tip over and break.
Put a sheet of paper on the floor under where the glass sits on the elevated surface.
Turn on your flashlight and shine the light through the glass, angling down to the paper on the floor. If you do not see a rainbow, adjust the light's angle.