It's easy...just build your script like this:
<script type="text/javascript">
google.load("visualization", "1", {packages:["corechart"]});
function drawCharts(){
var data1 = new google.visualization.DataTable();
var data2 = new google.visualization.DataTable();
<populate data1>
<populate data2>
var chart1 = new google.visualization.<chart 1
type>(document.getElementById('chart_1_div'));
var chart2 = new google.visualization.<chart 2
type>(document.getElementById('chart_2_div'));
var options1 = {<options>};
var options2 = {<options>};
chart1.draw(data1, options1);
chart2.draw(data2, options1);
}
google.setOnLoadCallback(drawCharts);
</script>
and you will have two charts.