Building simple machines and Rube Goldberg machines are some good non-electrical invention ideas for kids. Depending on the age group, many different inventions can be made with one or more of the six simple machines, including the lever, pulley, wedge, screw and incline plane along with the wheel and axle. For older kids, Rube Goldberg machines allow them to build non-electrical machines that combine many different simple machines and physics laws to make overly complex devices to perform simple tasks.
A send-a-snack machine is a type of non-electrical invention that younger kids might make using a pulley. The project only requires two thread spools, two pencils, 40 feet of string, a binder clip and a bag of chips. One student has a spool with a pencil through the middle, most of the string rolled onto the spool and a bag of chips clipped to the string in front of the spool. The string is stretched across the room, tied to a spool with a pencil through it and held by another child who winds the spool and moves the packet of chips.
Rube Goldberg machines are based on the satirical cartoonist that lampooned Americans love of technology. The machines can get as complex as a kid can invent. Inventions might include an elaborate plant watering device that uses a pendulum to swing into a can, causing it to roll across a table and knock over a bottle of water that pours through a funnel and waters a plant below.