Simple Machines: Wheel and Axle

Next column on our Machine Chart is the Wheel & Axle. We just talked about screws in our last column, but what would a screw be without a screwdriver? That's right...a screwdriver is a type of wheel & axle. The axle (rod) fits into the head of the screw & the handle serves as the wheel as it turns. Your hand supplies the force.

The wheel by itself is just a roller. It is useful because it can help do work with less friction, but it is not until you connect it to an axle does it really become a useful machine. Of course we automatically think of cars when we think of the wheel & axle...what others can you think of?

How about a doorknob? The rod through the door is the axle & the knob is the wheel. Once again your hand supplies the force & they all work together to move the latch. Wheel & axles move things easily & help make work easier to do.

Some other objects that fall under this category are gears. Gears are sets of wheels that work together. One wheel can work another wheel if they are notched together. When my son was little our McDonalds had a play table with legos & gear style building pieces. He & the other kids would put together elaborate sculptures & then they would turn one wheel which was connected to all the others & soon the whole thing had dozens of spinning wheels going at once. It was awesome! Sometimes us parents would jump in on the fun.

Bicycles work by one wheel turning the other one as well. This time a chain is used to connect the two. The larger wheel is connected to the pedals & then the chain connects the larger wheel to the smaller one on the front.

If you have a bicycle turn it upside down. Push the pedal slowly around with your hand. Watch the two wheels...one spins faster than the other, which one? The smaller one does. The larger wheel is connected to it making it move...it supplies the force. The speed of your bicycle is determined by how fast the front little wheel spins...the back wheel pushes the bicycle forward.

Can you find other wheels, axles, & gears around your home? How about an old egg beater (turned by hand), the inside of a watch (gears), a wagon, & a pencil sharpener (turned by hand). Remember to add photos to your chart & add any other items that you think of.