Why do concave lenses always form virtual images?

Plane mirrors, convex mirrors, and diverging lenses can never produce a real image. A concave mirror and a converging lens will only produce a real image if the object is located beyond the focal point more than one focal length away

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.