# Exploding Disk Cannons, Slimemobiles, and 32 Other Projects for Saturday Science

Neil Downie runs a Saturday science program for kids in Guildford, UK, that appears to be the most fun that anybody could have. This book is the third in a series that describes projects that he has invented for kids to build and investigate (often with the help of an adult). Most of the projects would ordinarily be classified as engineering, but several involve chemistry, and the science and mathematics are thoroughly described, along with helpful suggestions and pitfalls to be avoided. Along with new motors, transmissions, and detonators for balloons, this one includes a method of printing that uses electrolytic iodine to develop an image, a method of measuring the flow of dry materials via triboelectricity, a sensitive method for discriminating solvents on the basis of how they swell (and therefore change the conductance of) polyethene. The "slimemobile" is a vehicle that oozes along a flat surface on a of plenum of gelatin that is constantly injected under the bottom of car, and the "exploding disk cannons" of the title use compressed air to send a projectile when a disk between high and low pressure is fractured on command. All of Downie's books are consistent with the quote from Douglas Adams in his Preface: "I can't tell you anything ... you never believe anything unless you've worked it out for yourself."

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