[SOLVED] Conservation of Energy From 'Superstrings and Other Things' by Carlos Calle I understand and agree with everything up to where he says , shouldn't increase be decrease. I cant see how the bird can gain mass, only loose it by converting it into it kinetic energy? which would make sense. I might be missing the point completely or its simply just a printing error? This then lead me to thinking about us, when we move about, does the energy come from particles in our body undergoing reactions giving off energy, resulting in an overall decrease in our mass and increase in kinetic energy? and using E=MC^2 calculates the energy given off?