In addition to what I said earlier, gliders try to find lift to increase altitude/potential energy. When a high speed aircraft such as a Hawk loses the engine, for real or practise, the only way to increase potential energy is an exchange with kinetic energy. Alternatively, excess kinetic energy (speed) can be used to travel across the ground at constant potential energy. This is another fundamental difference.
With respect to glide angles, most aircraft such as the Hawk will glide gear and flaps up at about 2nm/1000 ft which, as flighthappens has said, is a still air glide ratio of 1:12. Once the gear and flaps are down, this reduces to about 1nm/1000 ft or 1:6.