First-Class Levers

Introduction

A lever is a simple machine used to make work easier. It can help you move heavy objects by increasing the force you exert. A lever consists of a long, rigid bar with a support that allows the bar to pivot. The point where the bar pivots is the fulcrum. There are three classes of levers: first, second, and third. A first-class lever looks like a seesaw. The effort (applied) force and resistance force (load) are at opposite ends with the fulcrum somewhere in between. Crowbars and scissors are examples of first-class levers. In a second-class lever, the effort force and the fulcrum are at opposite ends with the load in between. Wheelbarrows and nutcrackers are examples of second-class levers. When you do a pushup, your body is acting like a second-class lever with your toes as the fulcrum helping to lift your entire weight with your arms. In a third-class lever, the effort force is between the fulcrum and the load. Baseball bats, oars, and shovels are examples of third-class levers. Mechanical advantage (MA) is a value that tells the number of times a lever increases your effort force. Actual mechanical advantage (AMA) includes friction losses, while ideal mechanical advantage (IMA) does not. The difference between the ideal and actual mechanical advantage is a measure of the lever’s efficiency.

Objectives

In this experiment, you will

• Use a Force Sensor and NXT to measure the effort force required to pull a lever.
• Compare actual mechanical advantage and ideal mechanical advantage.
• Make conclusions about levers.