This week's free iPad app is Liquid Sketch, although it's only free for a limited time so I suggest you go out and get it now. Here's a brief summary as on the App Store:
Solve puzzles using beautifully colored, unbelievably realistic liquid. Rotate your device to pour, use your fingers to splash around or build bridges and pipes with blocks. Engage in 90 challenges testing your logic over 6 stages covering different aspects of liquid mechanics or let your imagination run wild in the sandbox mode.
LiquidSketch is truly an amazing puzzle game that has received a great rating on the App Store (4+). I personally rate it: