Always use the safety belt and buckle your child in immediately after putting her in the booster seat. Even if your child's belted in safely, never leave her sitting in a booster seat unattended. Hold off on using booster seats without belts, such as the plastic cube-shaped seats you often see in restaurants, until your child's about 36 months old. These seats are not only dangerous because they lack safety belts, but they're also missing straps for securing the booster to a chair.
Noun. 1. trough-a narrow depression (as in the earth or between ocean waves or in the ocean bed). natural depression, depression-a sunken or depressed geological formation. swale-a low area (especially a marshy area between ridges).
Waves have moving crests (or peaks) and troughs. A crest is the highest point the medium rises to and a trough is the lowest point the medium sinks to. Crests and troughs on a transverse wave are shown in Figure 1. Figure 1: Crests and troughs in a transverse wave. Definition 1: Crests and troughs. A crest is a point on the wave where the displacement of the medium is at a maximum. A point on the wave is a trough if the displacement of the medium at that point is at a minimum.