I took an average pebble out my garden. It weighs 10 grams and has a mean diameter of about 20 mm. If we assume it were perfectly spherical with a drag coefficient of 0.47, travelling through air with standard density of 1.225 kg/m^3, and plug the figures into the formula for terminal velocity we get: sqrt((2*0.01*9.81)/(1.225*(3.14*0.01^2)*0.47)) = 33 m/s or 119 km/h. If we pipe that into E = 1/2*m*v^2 for energy, we get ~5.5 J or ~4 ft-lb.

Or in other words, I need Bitcoin to do something exciting.