8 Joules is a really small amount of energy. I wouldn't be surprised if an average healthy child could put that much energy into a ball by kicking it. A quick

8 Joules is a really small amount of energy. I wouldn't be surprised if an average healthy child could put that much energy into a ball by kicking it. A quick back-of-envelope calculation says a 0.45kg ball (FIFA standard ball) traveling at 6m/s (~13MPH) has more than 8 Joules of energy.