A Rube Goldberg machine is a device that makes a simple task difficult. For example, you could turn off a light in twenty steps using a series of dominoes, a pot of boiling water and a stapler gun. Invented by cartoonist Rube Goldberg, these fanciful machines are meant to be a fun way to play with simple mechanics. The only catch is you cannot help it along in any way. Building one may seem challenging but can be done on a budget with a couple of household supplies. For this machine, we will shut a door in about four steps.
Set up a series of dominoes on a table or an elevated surface. Make sure that they are spaced close enough together so that they will hit one another. Build the line of dominoes up to the edge of the table. Also double-check that the table is close to a door.
Place a small strip to serve as a ramp at the end of the table. A miniature car ramp works best, but you can improvise with a thin piece of plywood or plastic. Place a marble at the head of the ramp; its motion will be triggered by the falling dominoes.
Mount a funnel on a stand at the bottom of the table. Make sure that the ramp meets the funnel. This will collect the marble and direct it to the mousetrap.
Place a mousetrap at the bottom of the funnel. Tie a string to the mousetrap then attach it to the doorknob. When the marble hits the mousetrap, the spring will activate, tugging the string and opening the door.
Test the machine's various steps to make sure they work. The transitions should successfully transfer force between steps. Do the dominoes hit the marble? Does the mousetrap properly connect with the doorknob via the string? These triggers are worth checking and rechecking.
Perform at least one or two test runs before you unveil the project. If one or two sections are not working, remove them rather than have a useless machine. The best Rube Goldberg machines are those that work without your intervention, not the ones that have the most steps but need a little help along the way.
If you do not have a stand for the funnel, improvise with objects around the house. For example, two tall books could hold up the funnel if placed on either side.