Drones: A drone is an aircraft that flies without a human pilot on board

The forces that act on a drone's movement include Aerodynamic force, which is the force of an object through air.

Drag is the force that an object feels as it passes through air.
Drag is affected by the speed the object is travelling.

Solar energy is the most common source of energy for drones.
When the drone is at rest, no energy is being used.
When the drone starts to fly, it uses electrical powered energy to move.
While in motion, drones transform electrical energy into kinetic energy.

Batteries: Some drones are powered by lithium-polymer batteries (LiPos) which only last for for about 20 minutes, depending on your load.

Solar power: Drones powered with solar power usually have solar cells attached to their wings.
They use solar power to fly when the sun is up, while simultaneously storing power in the battery for flying without sunlight as a source of backup power.

Hydro fuel cell: This fuel cell can take your drone for a spin for about two hours

Drones are being used for many reasons such as:

Drones currently have many uses like delivering stuff, crime fighting and covering sporting events.
Drones are presently used for numerous applications
ranging from insurance to emergency management and real estate and so on.

Drones could provide fast documentation for insurance claims.

Drones can put people out of risk when doing dangerous jobs involving environmental control and sustaining the environment.

Environmental agencies have adopted drones to catch polluters red-handed in the act of dumping or fly tipping. NASA have also started using drones to monitor the ozone layer and environmental consultancies have started using them for air pollution sampling.

One of the advantages that drones have is their low cost.

Drones could be used as an emergency deliverer in the future.
Drone delivery systems are in development and on the horizon as soon as the current legislation changes.

Drones can also be used for many things such as, crop inspecting, photography, deliveries, lifesaving, real-estate photography, and other things.

The use of drones is spread out over many nations.