A simple machine is a device that changes the direction or magnitude of applied force. The term is commonly used to describe six devices known to Renaissance scientists: the inclined plane, lever, pulley, screw, wedge, and wheel and axle. Complicated machines are composed, more or less, of parts derived from the simple six.
- Wood board
- Wooden doorstop
- One-foot ruler
- Paper-towel roll
A screw is a little hard to create from scratch. They used to be made of wood, as jack screws. A student that is particularly proficient at woodwork might be able to make the pieces, but it is not something that lends itself to being created from mere household items.
Attach a string to the inner radius of a doorknob. Twist the outer knob to coil up the string. This is a short-range version of a wheel and axle. The larger radius provides leverage. This leverage is the reason doorknobs are so large compared to their shafts, because of the high tension of the spring inside. Historically one of the more common wheel and axle machines was a crank on a cylinder that rolled up the rope from a well bucket. The crank (or wheel) provided the leverage, as the knob does here for the string.
Remove the string from a spool and nail it through the center to a wood plank. It can now function as a pulley, serving to redirect the lifting force of a line or string passed over it.
Use a wooden doorstop as a wedge. It could be used to split partially cut wood, using a hammer, a common use of the wedge in historical times. Scissors and axes also constitute wedges, for they transfer the large distance they travel into the material they're splitting into a small lateral distance of pulling the material apart, but with much greater force.
Place a ruler on a used-up paper towel or toilet paper roll. This constitutes a lever, with the cardboard roll serving as the fulcrum. By making the end that is lowered longer, the shorter end exerts a greater force on any load it lifts.
Stack a flat piece of wood board onto a short stack of books. This constitutes an inclined plane. If a spool is affixed horizontally over its edge, it can demonstrate, as a pulley, the value of the inclined plane. Connect two small weights of equal mass linked with string. Place one weight on the inclined plane. Drape the other over the spool and hang it off the side of the stack of books. The hanging weight will drop, pulling the other weight up the incline, demonstrating the increased ease of levitation when an inclined plane is used.
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