Book excerpt: How do machines work? Kids will have a blast constructing a mini-seesaw to illustrate the way a lever operates or creating their very own pulley from an empty spool, string, ribbon, pails, pennies, a broom, and two chairs. They’ll find out why they can’t put in a screw using only their fingers and examine the different parts of compound machines. In another experiment, a child’s bicycle becomes a laboratory for understanding whether wheels have to be smooth to run. A good time will be had by all.