We thought that Crayon Physics would be just perfect for the DS, and apparently, we weren't the only ones. In fact, the game has even inspired homebrewer 0xtob to make a similar application for the DS, called Pocket Physics. The homebrew might not be nearly as fleshed out as the original, and it's more of a demo than an actual game, but we still love it.
To understand the gist of Pocket Physics, watch the (low-quality) video of someone playing it after the break. You can also check out the program for yourself here.