mysql_query isnt working

I have a form that is suposed to insert a new record in to the db when someone clicks on the submit button

I think i have it set u p correctly her is my page

 if (isset ($_POST['post'])){
    $tanounce = $_POST['announcements'];
    $announce = trim($tannounce);
                if ( !empty($announce) ) 
mysql_query("INSERT INTO `impactathletics`.`team` (`announcements`)
WHERE team_id = '1' 
VALUES ('$announce')");
            <form method="post" action="<?php echo $_SERVER['PHP_SELF'] ?>">
                <textarea name="announcements" cols="45" rows="5"></textarea>
                <br />
                <input type="submit" value="Submit" />
                <br />

can any one see the problem?
side note the table its supposed to be inserted into already contains info. Will it add to the field? or will it drop it.