Looks to me like its just the downward force of the magnet vibrating the glass like a spring board, thus shaking the pennies out. Notice the 'stronger magnetic force' nearer the edge where the vibrations are largest. I'd prefer to see it with the glass firmly mounted not touching the pennies.
Stay up to date on the latest news of the future of science and technology from your iPhone with full articles, images and offline viewing
Featuring every article from the magazine and website, plus links from around the Web. Also see our PopSci DIY feed
Share links with friends, comment on stories and more
In our December issue, Popular Science names the 100 best innovations of the year: bombproof wallpaper, self-parking cars, the fastest helicopter, and 97 more. Plus inventor profiles and videos.
Check out the best of what's new here.