As any educator will tell you, exploration is key; witness the generations of children who have been introduced to basic math and science concepts at sand and water tables. Tinybop, a Brooklyn, NY, based developer, has taken this principle to heart with their sandbox apps. In The Human Body, viewers watch as the cookie that they deliver to a  child's mouth travels through the X-ray view of the figure's digestive system, or learn how the body reacts to an insect bite (an insect they have let loose). In Plants, children can observe how the landscapes and denizens of various biomes change as day becomes night, the seasons change, and various user-triggered weather systems move in. In Simple Machines (iOS, $2.99; K-Gr3), kids have an opportunity to explore the forces at work in the lever, wheel and axle, pulley, inclined plane, screw, and wedge. For each one, viewer-controlled interactive options allow them to see how various adjustments impact the machines' mechanics or force. For example, by altering the location of the lever's fulcrum, the distance a load can be projected will change, while the height, base, and height from which a wedge is driven will affect its efficiency. In "Wheel & Axle," users can try four bicycles or scooters and adjust the speed at which the creature riding them travels; at a fair clip, rider and vehicle sail over a narrow stream of water or up and over a ramp, but if they're moving too slowly the front wheel will plunge into the water or the creature will fall forward. The colorful settings (art by James Gilleard) are pure whimsy and add to the game-like activities: the inclined plane page is designed as a pinball machine, the load of the lever is aimed at a castle, and the pulley screen (which allows kids to try four different arrangements of fixed and movable pulleys) resembles an arcade game. Users can switch scenes from day to nighttime lighting, which changes the view in various, mostly small, ways (colors of arrows change, or on one page, the view of fish becomes an x-ray view). There are no in-app instructions, but the activities are fairly intuitive and play and exploration are rewarded. Sound effects (chirping birds, whistling wind, etc.) and atmospheric music, add to the fun and offer an element of play as well, but can be switched off. The app contains no text, however, labels for the illustrations are provided in five languages (English, Spanish, French, German, and Chinese), and the iTunes store lists dozens more. A free, downloadable handbook (in seven languages) contains extensive notes on the science behind these machines, tips on using the app with kids, and additional suggested activities. For today's students, digital sandboxes create additional, hands-on opportunities to explore concepts. Use this app as an adjunct to science lessons, or download it onto the classroom iPad for some free play; understanding of basic physics concepts is sure to follow. A trailer is available.—Daryl Grabarek, School Library Journal  

Screen from the "Wheel & Axle" page of Simple Machines (Tinybop) Gilleard

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