Should I use an apostrophe for slang contractions?

Hello,

I am writing a lyric sheet for some finished songs. I want to write exactly what was recorded not what is grammatically correct.
I can't determine if I should be using an apostrophe or not. Here are some examples:

The works hard = the work is hard. Should it be written as - the works hard or the work's hard

My left sides hurt = my left side is hurt. Should it be written as - my left sides hurt or my left side's hurt

Lifes known as absurd = life is know as absurd. Should it be written as - lifes known as absurd or life's known as absurd.

I think that I should consistently be using an apostrophe in these situations but I could be wrong. Could somebody let me know what the correct way to write this is?

Are there any rules for determining what I should do?

thank you,
Frank

[Barb_D]

Hi Frank,
Continue to use the apostrophe to show the contracted form of "is."

The work is = The work's
My side is = My side's
Life is = Life's

I would add that these are not "slang contractions" but extremely common used at every level of spoken English and omitted only in the most formal types of written English.

{not a teacher}

[konungursvia]

Agree with Barb....

[Soup]

Hi

I agree with Barb as well, and here's the rule:

An apostrophe replaces a letter:

1. the work is hard / the work's hard <' replaces i>
2. my left side is hurt / my left side's hurt
3. life is know as absurd / life's known as absurd.