You can draw two charts within a single function:
function drawCharts() {
var data1 = new google.visualization.DataTable();
<populate data1>
var data2 = new google.visualization.DataTable();
<populate data2>
var chart1 = new google.visualization.ColumnChart(document.getElementById("chart_div_1"));
chart1.draw(data1, <options>);
var chart2 = new google.visualization.ColumnChart(document.getElementById("chart_div_2"));
chart2.draw(data2, <options>);
}
The div ID's are arbitrary; use whatever you choose to name them in the HTML.