Miami ? When University of Central Florida junior Nicole Nissim got stumped in trigonometry, she checked out what was showing on YouTube.

Nissim typically scours the video-sharing Web site for clips of bands and comedy skits. But this time she wasn’t there to procrastinate on her homework. It turned out YouTube was also full of math videos. After watching a couple, the psychology major says, she finally understood trig equations and how to make graphs.

“I was able to watch them at my own pace and if I didn’t get a concept, I could easily rewind it,” Nissim says. “It was a lot clearer once I watched the video.”

YouTube is perhaps best known for its cavalcade of homemade performances and TV clips, but many people like Nissim are turning to it for free tutoring in math, science and other complicated subjects.

Math videos won’t rival the millions of hits garnered by laughing babies, but a YouTube tutorial on calculus integrals has been watched almost 50,000 times in the past year. Others on angular velocity and harmonic motion have gotten more than 10,000 views each.

The videos are appealing for several reasons, says Kim Gregson, an Ithaca College professor of new media. Students come to the videos when they’re ready to study and fully awake — not always the case for 8 a.m. calculus classes. And they can watch as many times as they need until they understand.

Viewer comments reflect that. On tutorials posted to YouTube by the not-for-profit Khan Academy, for example, reactions include: “Now why couldn’t my calc instructor explain it that simply?” and “I was just about to leave my physics course. You saved me.” One viewer went as far as to declare to the man behind the videos: “You are god of mathematics!!!”

YouTube’s potential for instruction is one reason Internet search leader Google Inc. bought the video site for $1.76 billion two years ago. Google founders Sergey Brin and Larry Page realized that certain search requests could be better fulfilled with how-to videos than with written explanations.