Trailer

A Trailer is normally an unpowered vehicle pulled by a powered vehicle, because powered trailers are more explicitly called pot railers. Commonly, the term trailer refers to such vehicles used for transport of goods and materials. Trailer winches are intended to load (or unload) boats and other cargo to and from a trailer. The are invented a ratchet mechanism and cable. The handle on the ratchet mechanism is twisted to tighten or loosen the tension on the winch cable. There are both manual and motorized trailer winches

Popup campers are trivial, aerodynamic trailers that can be towed by a small car, such as the BMW Air Camper and the Coleman Bayside. They are built to be shorter than the tow vehicle, minimizing drag. Others range from two-axle campers that can be pulled by most mid-sized pickups to trailers that are as long as the host country's law allows for drivers without individual permits. Larger campers tend to be fully integrated leisure vehicles, which often are used to tow single-axle dolly trailers to allow the driver to bring small cars on their travels.

Rainbow

Rainbows can be practical whenever there are water drop in the air and sunlight shining from behind the observer at a low altitude or angle. The most spectacular rainbow displays when half of the sky is still dim with draining clouds and the observer is at a spot with clear sky overhead. The rainbow effect is also commonly seen near waterfalls or fountains. Rainbow fringes can sometimes be seen at the edges of backlit clouds and as vertical bands in far rain or virga. The effect can also be artificially created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or night-time rainbow, can be seen on stoutly moonlit nights. As human visual observation for colour is poor in low light, moonbows are most often perceived to be white.
The rainbow's exterior is caused by dispersion of sunlight as it goes through raindrops. The light is first refracted as it enters the surface of the raindrop, reflected off the back of the drop, and over refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40°–42°. The angle is self-determining of the size of the drop, but does depend on its refractive index. Seawater has a higher refractive index than rain water, so the radius of a 'rain'bow in sea spray is smaller than a true rainbow. This is visible to the naked eye by a misalignment of these bows.

Reverberation

When active sonar is used, spreading occur from small objects in the sea as well as from the bottom and surface. This can be a main source of interfering but does not occur with passive sonar. This scattering cause is different from that in room reverberation which is a reflection incident. An analogy for reverberation is the diffusion of a car's headlights in fog or mist. A high-intensity pencil beam will break in the fog; main headlights are less directional and where the returned noise dominates. Similarly, to overcome reverberation, an active sonar requests to transmit in a narrow beam.