Energy can exist in two main forms - kinetic energy, which is the energy of motion, and potential energy, which is the energy due to an object's position or shape. Kinetic energy depends on an object's mass and speed, and can be calculated using the equation KE=1/2mv^2. Potential energy includes gravitational potential energy, which depends on an object's weight and height above the ground and can be calculated as GPE=mgh. Mechanical energy represents the total energy of an object, including both its kinetic energy and potential energy.