Approximants

Approximants

Approximants are sounds made by narrowing the oral cavity but not enough
to cause turbulence in the airstream; the airstream is said to be smooth. The
beginning sounds of lye and rye are approximants. The narrowest point in
the airstream is wider in approximants than in fricatives, but is not as wide
as it is in vowels. Approximants are more sonorant (resonant, i.e., naturally
loud) than consonants, but less so than vowels. They are like consonants in
that they typically occur before or after the vowels of syllables (see below).
English has three kinds of approximants.

Lateral 

approximants are made by touching the tongue to the alveolar

ridge while allowing the air to pass along one or both sides, as in [l]—inlack, call, and callow.

Central

 approximants are made by raising the sides of the tongue so that
the air flows along the center of the tongue, as in [r]—in rock, roll, and Rory.
[r] is regarded as an alveolar sound.

Glides (semivowels)

come in two kinds: palatal and labio-velar. Palatal glides are made by raising the tongue toward the hard palate, close to where the vowel in eat is made. The first sound of yet, yolk, and y’all is a palatal glide, represented phonetically as [j]. Labio-velar glides are made by rounding the lips and simultaneously raising the back of the tongue toward the velum,

close to where the vowel sound of ooze is made. Labio-velar glides thus have

two places of articulation—they are both labial and velar. The first sound of
wet, wall, and wink is a labio-velar glide, represented phonetically as [w].