There are lots of different types of energy:
Kinetic, gravitational, elastic, heat, light,....
It is one of the the fundamental principles of physics that total energy is conserved. When energy transfer occurs, the energy we start with is transformed into another form of energy. The energy never just disappears. If some of the energy appears to be wasted, then that energy has been used to overcome forces like air resistance or friction. If this happens some energy has become internal energy of some substance,- heat - but it has not disappeared.
For each form of energy there are equations to tell us how much energy there is. If a body of mass m has velocity v then it has kinetic energy given by
A body of mass m is at a height h above the floor then it has gravitational potential energy given by
As the skateboarder moves from position 1 to 2 in the diagram, his kinetic energy changes into gravitational potential energy. At 3, all the kinetic energy the skateboarder had initially has been changed into gravitational energy. In fact there is friction to be overcome, and the skateboarder's gravitational potential energy at 3 will be less than that show. In practice this will mean he will not quite rise to a height of 3.27m.
