Work and Machines

This section introduces an important concept that the work put into a machine is equal to the amount of work that is produced by the machine. After reading this statement, discuss briefly the image of the lever. The finger is pushing down. This "effort" is a certain amount of work. As a result of this work, the lever (the machine) is doing the work by lifting the load. These two amounts of work are equal – at least in theory. Of course, some energy is lost in the system, mostly by friction.

This section discusses that although work may be equal in two systems, some tasks require more force. The Turn and Talk requires a quick discussion. Most students will realize that the steepest slope has a shorter distance for the bike to travel, but requires much greater force. (Just for fun, you may want to ask students if they could bike up either slope. Perhaps the work required for the steeper slope isn’t possible!)

The slide refers to lever systems. This lab activity is in The Clever Lever.

Paraphrase:

So, you might think, why do we care about machines if they don’t do work for us? Well, here’s the thing: machines can take work that’s hard for us to do and make it easier by shifting it around.

Read together the thought bubbles and emphasize that many complicated machines use electrical or gas power. You may wish to challenge students to list human-powered tools such as skateboards, ice skates, pole vaulting, a swing, a child’s pedal car, a scooter, a pencil, a screwdriver, a hammer, etc.

To elicit more responses, you could take time to list them by categories such as writing tools, construction tools, transportation, and toys.

Some of the tools you list are, combine, or include examples of the six simple machines defined by Archimedes.