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).
(Amplitude is the distance from the rest position to the crest position which is half the vertical distance from a trough to a crest.). (Wavelength is the distance from crest to crest, which is twice the horizontal distance from crest to nearest trough.). (The period is the reciprocal of the frequency.