Gears: Lift It Up!
Two sixth-grade students using the LEGO pulley and gear setup for the activity.
A gear is a simple machine that is very useful to increase the speed or torque of a wheel. In this activity, students learn about the trade-off between speed and torque when designing gear ratios. The activity setup includes a LEGO® MINDSTORMS® pulley system with two independent gear sets and motors that spin two pulleys. Each pulley has weights attached by string. In a teacher demonstration, the effect of adding increasing amounts of weight to the pulley systems with different gear ratios is observed as the system's ability to lift the weights is tested. Then student teams are challenged to design a gear set that will lift a given load as quickly as possible. They test and refine their designs to find the ideal gear ratio, one that provides enough torque to lift the weight while still achieving the fastest speed possible.
Gears are a fundamental element of many machines. Gears transmit power and can be used to gain the mechanical advantage necessary to lift a heavy load, or simply speed up a process if the load is light. Mechanical engineers use gears when designing machines such as bicycles, elevators and automobiles in order to increase the speed of a device, or its ability to pull or lift heavy objects. When mechanical engineers design devices with gears, they choose gear sets based on specific design requirements, keeping in mind how different gear ratios affect a system's performance.
After this activity, students should be able to:
- Describe the relationship between gear ratio, speed and lifting ability.
- Calculate a gear ratio.
- Choose gears for a gear set that optimizes lifting speed for lifting a given load (weight) and test the gear ratio.