Let's analyze two little words together? Are they:
HURT AND BOARD
Is there any similarity between them?
Again we will carry out one more experiment: are we going to pronounce them?
Ah! and what happened?
As we can see, the second syllables of these words, when pronounced (of course, we are referring to oral language here), reveal the same sound, that is, both seem to be written with a “u”. And did you know that this is exactly why we sometimes have some doubts when it comes to correctly writing the many words that exist in the Portuguese language? Remember the “x” and the “ch”, the “s” and the “z”?
But actually, even if there are, yes, some similarities between the words, what we should know is that there are specific rules for each group of them, as also happens with those that constitute the two vowels that we have already mentioned, that is, there are circumstances in which we must use only the letter "O"; and others, only the letter “u”.
Are you finding it a little complicated? Don't worry, as soon as we'll find out where they are. Let's go then?
We write with "o":
almond
pile up
Swallow
throat
hurt
gizzard
schoolbag
kid
stain
Cooked Corn Meal
mosquito
toilet
to cough
penny, making fun, among others.
We write with "u":
bonus
manhole
mouse
agouti
embed
clog
tortoise
jabuticaba
jaw
board
times tables
board
nettle, etc.
Let us now recall a subject of which we are already aware... do you remember the paronyms? They are similar in writing and pronunciation, but which are different in terms of the meaning they represent. Well, there are some of them, which are also written with these same vowels, that represent this case. Therefore, we will now look at some examples:
length (extension)
The length of the dress is long.
greeting (greeting)
The birthday boy received several greetings.
sound (beep)
The school bell has already rung, it's recess time.
sweat (perspiration)
We sweat a lot when we play ball.
sort (stock)
The fridge is stocked with delicious treats. 
arise (result)
The conversation with the teacher resulted in the good result I got in the test.
By Vânia Duarte
Graduated in Letters
Kids School Team