(CNN) -- Brittany Wenger learned about artificial intelligence during a seventh-grade school project. She was immediately enthralled, bought a book on programming and taught herself how to code.
Now 17, Wenger won the grand prize at the second annual Google Science Fair on Monday for her project on improving breast cancer diagnosis accuracy using artificial neural networks.
That combination of drive, passion for science and a desire to do something good was common at this year's event. Organizers of the online science fair received thousands of entries from 100 countries, including India, Ukraine, Malta and Swaziland. Google picked 15 finalists and, at a final gala in an airplane hangar in Palo Alto, announced the winners in three age categories, along with a grand-prize winner.
Jonah Kohn, 14, won first place in his age group for a project that helps people with hearing loss experience music through vibrations. A team of three 15- and 16-year-olds from Spain took home a trophy (made entirely out of Legos) for their look at the microscopic creatures that thrive in fresh water.
Two 15-year-old young men from Swaziland researched hydroponic techniques to help subsistence farmers in their homeland, where food shortages are a devastating problem. They won the Science in Action award, which highlighted a project making a practical difference.
Before the winners were announced, the finalists presented their projects one last time on the Google campus Monday afternoon. Groups of young kids from summer camps filed through to meet the young scientists and watch their demonstrations. Some Google employees even brought their children to work for the day just to see the event.
In classic Silicon Valley fashion, many adults were there grilling presenters, just like they would any entrepreneur with a pitch. They asked tough questions about methodology, costs and results. Some even asked about business plans.
One man urged finalist Rohit Fenn to make his eco-friendly toilet design, the Vacu-flush, open source. Fenn's prototype uses a vacuum system that consumes 50% less water than traditional toilets. Unfortunately, his design is still too cost-prohibitive to be made made without the help of established toilet manufacturers.
"They would need to take me seriously, which they won't because I'm 16 years old," he said.
The contest was free to enter and open to all students around the world between 13 and 18 years of age. Google collected entries from January to April and announced the finalists in May. The grand prize winner receives a $50,000 scholarship, an internship and a trip to the Galapagos Islands.
For Wenger, one of the highlights of the experience was meeting famed computer scientist Vint Cerf, who talked with her at length about computer science and neural networks.
For her winning project, Wenger wrote a program that improves diagnoses of malignant breast tumors by using a large amount of data stored online and looking for patterns. It's an ambitious project that was made possible by that first spark of interest in programming five years ago
"I decided that it was what I was going to do," said the Florida native. "I'm very persistent, and I learned to code, and I started coding neural networks that played soccer -- I'm an avid soccer player as well."