There is only one species of emu (that is not extinct) and it does not have a crest, or helmet. None of the other ratites has a helmet.
crest
There are a great many different Smith families. Most will not have a family crest since most blacksmiths, copper-smiths and the like were not in the social classes that had crests. Any two that do have family crests will have different crests.
I assume you mean, the crests of a wave. That distance is called the wavelength.
Surnames don't have family crests; families have family crests. For any given surname there can be several unrelated families, each with a different crest, and many more unrelated families with no crest at all.
Yes. Actually, there are two different crests. You can find them by Googling "selwyn family crest" (no quotiation marks).
In a wave train, the distance between successive wave crests is called the "wavelength".
The highest parts of a transverse wave are CRESTS.
Certainly. Very few families actually have family crests.
Between the tops of two crests, there is a trough marking the lowest point.
usually 1 - a crest is the highest tip of a wavelength. But if the wavelength is measured from the highest point them in 1 wavelength there will be 2 crests
Most Ward family crests that can be viewed by Googling "ward family crest" do not have any animals on them. A few have a horse.
it depends on what you are talking about if your talking about light here it is light can be classified as a wave when your talking about crests and troughs a crest is the top most part of the wave if you split the wave in half the trough has the same principle it is the lowest most part of the wave if you split it in half does that clarrify a little bit?