The Magician's Catapult
In this activity, students reinforce their understanding of compound machines by building a catapult. This compound machine consists of a lever and a wheel-and-axel. Catapults have been designed by engineers for a variety of purposes — from lifting boulders into the air for warfare to human beings for entertainment; the projectiles in this activity are grapes for a magic act. Given the building materials, students design and build their catapult to launch a grape a certain distance.
Figure 1. A student-constructed catapult, ready to fire!
Simple machines and compound machines are the foundation of many modern conveniences. Engineers use a combination of levers, wedges, screws, wheels-and-axels, pulleys and inclined planes to develop simple tools such as a pencil sharpener to complex machines such as an elevator or airplane. Compound machines are everywhere. Engineers usually design machines for a specific function, as specified by their clients. Engineers also have to design within certain constraints, including time, money and human resources.
After this activity, students should be able to:
- Use the engineering design process to create a compound machine – the catapult.
- Describe the interrelationship of the simple machines within a compound machine.
- Describe the constraints of their model in the context of engineering.