Select Earth in the menu box so that there is now a force of gravity. Now the total energy of the weight/spring/Earth system is the sum of the kinetic energy, the elastic potential energy, and the gravitational potential energy. When is the kinetic energy a maximum? (It may help to watch the simulation in slow motion). Select Earth in the menu box so that there is now a force of gravity. Now the total energy of the weight/spring/Earth system is the sum of the kinetic energy, the elastic potential energy, and the gravitational potential energy. When is the kinetic energy a maximum? (It may help to watch the simulation in slow motion). When the mass is at the equilibrium position When the spring is at its unweighted length (its equilibrium position without the weight attached) When the spring is most stretched or most compressed