Brothers & Energy

A couple summers ago, my brothers, their friends, and I went out to the Mokolua Islands in Lanikai and jumped off the rocks at Shark's Cove. In this picture, my brother Ian is in the air and my brother Haakon is standing up on the rocks waiting to jump. Ian has both potential and kinetic energy. Ian's potential energy is with respect to the water, as soon as he jumped off the rock, his potential energy started to transfer to kinetic energy, and as he gets closer to the water his potential energy will get smaller and smaller. Potential energy can be negative or positive, depending of the reference level, and because my reference level is the water, Ian will have negative potential energy once he hits the water and goes under. The equation for potential energy is PE=mgh. Haakon is not in motion, so his velocity is zero, so his kinetic energy is zero, because KE=1/2mv2. All of Haakon's energy is potential. However, once Haakon jumps off the rock his potential energy will begin to transfer to kinetic energy, just as Ian's did. In a closed system, total energy is always constant and TE=PE + KE. PE can be negative or positive, depending on your reference point, but KE is always positive. An object only has KE if it is in motion.