You are camping with your family and your best friend. You’ve had a day of fun. Now you look forward to a night next to a blazing campfire. And it’s your turn to help start it!
You and your friend gather some logs. You crisscross them in a small pile. Your aunt tries to light one of the logs with a match. Nothing happens. She smiles. “We need smaller pieces of wood.”
But how? The wood is too hard to break apart with your hands. “We need a tool,” your friend says.
You remember seeing a small axe in a box of camping equipment. It’s the perfect tool for the job!
You bring it to your aunt. She stands a log up and carefully swings the axe so that the blade strikes the cut wood on top.
THWACK! The log splits to its halfway point. Another swing, and CRACK! It splits in two. A few more whacks reduce the half logs to pieces small enough to start the fire.
The axe is a good tool to split wood. It’s a simple machine. Simple machines help us do jobs. They move things faster, farther, or more easily than we can without them.
You probably don’t think of an axe head as a machine. A blender or a car might come to mind. These are all complex machines. They have lots of parts.
Simple machines have just a few parts. Some are made of only one part. Nearly every machine, however, has one or more simple machines.
Simple machines can be combined in endless ways to do tasks. But each one helps us do work all on its own.
A Wedge Gives You an Edge
The axe head that you used to split the wood is a simple machine called a wedge. It’s shaped like a triangle. The head starts out wide and narrows to a thin edge. The thinner the edge, the sharper the wedge.
How does it work? It starts with effort from you. It takes effort to swing the axe. This effort provides the force to drive the axe into the wood.
Swing the axe. The force is downward. As the axe pushes into the wood, the wedge directs that force sideways. Swing again and CRACK, the wood splits.
With a powerful CHOP, this axe splits the wood in two. The axe head is a wedge.
It’s All About Trade-offs
Now, suppose you had two axes to choose from. One has a head that is long and narrow. The other is shorter and wider. Which would you choose?
Remember, the thinner the wedge, the sharper the edge. The long, narrow axe head will be sharper.
So, it will be easier to drive into the wood with each swing. But it has to go deeper before it splits the log. The short, wide axe could split the wood without going in so deep. This might mean fewer swings. But each swing would need a lot more force. You trade distance for effort.