Scissor Lift physics

Key concepts
Physics
Mechanics
Linkages
Geometry

Introduction
Have you ever wanted to reach something way up high on a shelf? Or have you ever watched construction workers who need to reach up a tall utility pole? A scissor lift is a device that can extend to a great length but also fold up very compactly. In this project you will build your own scissor lift from common household materials!

Background
Mechanical linkages are a type of machine generally made up of rigid bars connected to each other by rotating or sliding joints. When combined, links and joints can be used to create many complicated motions that are used in machines all around you. They can be used to convert motion from one type to another. For example, a linkage in a car engine converts the back-and-forth motion of the piston to rotational motion, which is eventually transferred to turn the car’s wheels. Linkages can be used to amplify both force, such as in a pair of pliers, and motion. An example of the latter is if you have a lever in which one side is twice as long as the other, when you push down on the short end, the long end will move twice as far. (Note that in both cases energy is conserved—you can never get “free” work out of a linkage.)

In this project you will build a mechanism called a scissor lift. Such lifts are used in construction equipment to elevate workers to high places. More generally, they are a type of pantograph. A scissor lift uses an accordionlike motion to contract and stretch out, allowing it to both fold compactly and extend much beyond its original length. Try this project to build your own—and see what heights you can reach!

Materials

• Corrugated cardboard
• Pushpins or thumbtacks
• Modeling clay or Play-Doh
• Scissors (and an adult to help cut and use pushpins, if necessary)
• Ruler (optional)

Preparation

• Cut the corrugated cardboard into at least six equal-size strips. The exact dimensions do not matter but roughly two to three centimeters wide and 10 to 15 centimeters long is a good start.