As indicated in its name, the hoverboard moves suspended in the air.
It seems that an unknown force maintains it at about 4 inches (10 centimeters) above the ground. A little impulse with your feet on the ground is enough to make it slide like a skateboard, but in the air !
On its back, you can see 2 cylindrical flat shapes firmly maintained on the board. They look like magnets. It makes no doubt that those 2 cylinders actually allows the hoverboard to stay suspended in the air.
The hoverboard's principle is not really to escape the Earth attraction. Actually, it never lets a solid or liquid surface approach its back closer than a few inches. It's a repulsion system, like 2 magnets do when you confront the two same poles (++ or --). The difference here is that the surface in opposition can be made of various matters (concrete, earth, water, roc, wood, vegetation, metal, plastic...). However, the hoverboard doesn't work as well on the water. It seems to be slowed by liquid surfaces. Moreover, the foot impulse that is needed to move it cannot be done on water.
A most surprising thing is
that the board never turns over !
It is extremely stable. whatever the weight the board supports, it
stays always at the same distance from the ground. May it has to
support Marty's weight or a little girl's, the board seems to always
float at the same height. When Marty jumps on the hoverboard, we can
only see a slight movement of the board.
The incredible steadiness of the hoverboard is showed on several occasions :