Geothermal energyGeothermal energy A P F 20 minutesCold water is allowed to run into gravel which has been heated to just below 100oC. The temperature of the outflow is measured and its decrease with time noted. The rate of flow is measured by using a measuring cylinder and a timer. Put the gravel in a displacement can or better a saucepan. Hot rock E P F 40 minA rock which has been heated to just below 100oC is placed in cold water in an insulated container. The change in temperature of the rock and the water is measured and the specific heat of the rock and thus how much energy can be obtained from it is calculated.Hot granite DTo explain why granites are still hot and can be a source of geothermal energy use a piece of granite which is slightly radio-active and a Geiger counter.