Normally OS in the iPad is firmly. However, That can happen about hang or iPad frozen on screen. You should know how to restart it. If you know how to restart iPad that you will use with iPod and iPhone 4.
Let's press sleep/wake button on the top of iPad and home button together about 10 second. You will see red slide bar on the screen. Just press and hold onto that iPad will restart. Turn on power your iPad again by press sleep/wake button on the top.