Change files names

HI,
Is there any possibility to change names of many files using "mv" and "for" loop ???

For ex. I have many txt files.
file1.txt
file2.txt
...
And I tried something like this, but it's not working

for (( i=1 ; $i<=10 ; i++ )) ; do
mv file$i.txt newfile$1.txt;
done 

You have used 'newfile$1.txt', did you mean 'newfile$i.txt'?

Fix typo and try again

Oops ... It's so embarrassing :o
... but thanks for perceptiveness