Introduction

Middle school teachers can meet many science content standards and build on their students’ elementary knowledge of simple machines by studying these machines in terms of Newton’s laws of motion. In elementary school, students usually learn the different types of simple machines and may understand that simple machines make work easier.

Your students may already be aware of these ways that work is made easier: Pushing a heavy load on wheels is easier then pushing it across the floor without wheels. Raising a heavy load is easier with a pulley than trying to lift it with human muscle only. Walking up a ramp requires less effort than trying to jump straight up to the same height. Catapulting an object sends it further and faster than a human being can throw it.

Simple machines make work (work = force x distance, W = fd) easier by decreasing the effort (EF) needed to lift a resisting load (RF), but simple machines simultaneously increase the distance over which that effort (ED) must be applied to move the load (RD):

EF x ED = RF x RD, where EF < RF and ED > RD

(This is an idealized equation. In reality, some force is transferred to the pivot point via kinetic energy, where it is converted to heat energy and dissipated to the environment.)

In middle school classes, Newton’s laws of motion are presented as three distinct concepts, but of course, all three are in action any time an object experiences a force that may or may not be enough to send it into motion. For example, when a skateboard rider applies a force to the ground with one foot to overcome the skateboard’s inertia and to accelerate the skateboard (1st law), the ground pushes back (3rd law), and the skateboard and rider accelerate in the direction of the ground’s applied force at a rate inversely proportional to the mass of the earth (2nd law). The skateboard is doing the work of a simple machine in that it is experiencing force over a distance, W = fd. Any object we use for work or pleasure can be described in terms of the work it accomplishes.

So the skateboard is capable of doing work. That implies it is a simple machine. Which one? Or might it be a compound machine, a combination of two or more simple machines in which force is transferred between the various simple machines involved? The answer is that it is a compound simple machine: a lever combined with wheels and axles.

What if your skateboard had only two wheels, not four? What if it could go uphill without one foot pushing off the street? Then you wouldn’t have a skateboard, you’d have a wave board! And you’d be "street surfing," not skateboarding. So why not call it a "street surf board?" After all, there are no waves in the street. Or are there? The wave board requires the rider to generate mechanical wave motion in order to roll. Can your students relate its technology to the science of simple machines?

Humans have been making and using simple machines for work and pleasure throughout history. We cannot imagine life without them. But who were the first clever technologists? What is the science behind their technology? What science do modern technologists use when designing and constructing simple machines today? What science will your students use when inventing their own technological innovations?

The study of simple machines is especially attractive for autumn, when students are just returning to school, perhaps reluctantly, and have a new group to get acquainted with. The mild weather means learners can get outside to conduct some of these activities, putting a positive spin on school and science. Many activities require teamwork, conducive to relationship building, enhancing your class’s sense of community.

This publication highlights a breadth of resources, lessons and activities you can use to address the standards appropriate to your teaching content through simple machines.

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Copyright June 2007 — The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0424671. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

This work is licensed under a Creative Commons License.