Turn, turn, turn
How many wheels do you use in a day?
You can count wheels that roll—bicycle wheels, car wheels, and bus
wheels, too. They help you get places. A push from you or an engine
makes the axle turn. And the axle makes the wheels go around. The wheels
are much bigger around than the axle, so they roll a long way each time
the axle turns. The wheels help to get a lot of speed and distance from
each turn of the axle.
But you can count other kinds of wheels, too—wheels that don’t roll.
These wheels help you to do other kinds of work. A doorknob is a kind of
wheel-and-axle machine. The knob is the wheel! You turn it to make the
axle pull back the latch so the door can open.
A pencil sharpener has a wheel and axle, too. The handle may not look
much like a wheel, but it really is part of one. When you turn the
handle, it turns an axle that makes the other parts work.
A doorknob, a pencil sharpener, a can opener, and many other things with
handles that turn, all work in the same way. When you use these
machines, you are turning a wheel to make an axle move. The axle doesn’t
move fast or far, but it helps you get a lot of work from each turn of
the wheel.
