What is the working principle of a DC motor?

The working principle behind any DC motor is the attraction and repulsion of magnets. The simplest motors use electromagnets on a shaft, with permanent magnets in the case of the motor that attract and repel the electromagnets. The reason for using electromagnets is so that it is possible to flip their magnetic field (their north and south poles).

So the electromagnet is attracted to one of the permanent magnets. As soon as it reaches the permanent magnet, it’s north and south poles flip so that it is repelled from that magnet and attracted to the other permanent magnet. This video shows you the parts and how they fit together:

It is possible to get even simpler, although at that point the motor changes from being useful to merely instructive, as shown here:

The key to this demonstration motor is the fact that the insulation coating on the wire ends is only removed from one side of one of the wires

How does a mirage work?

This video does a nice job of showing what mirages look like. A mirage causes a road or a desert to shimmer like water, and to reflect objects in the distance:
The mirage effect is caused by a form of lensing created by hot air. The air right near a road’s surface can be very hot in the summer – much hotter than surrounding air. This hot air is much less dense than the surrounding air, and changes in density can affect how light travels. In the same way that light bends as it moves through water or glass, it can bend as it moves through different air densities. Because of the bending, light that would normally go toward the ground gets bent upward and into your eyes, creating what appears to be a reflection.