Simple Machines: Wheel and Axle
Simple machines help make work easier for people. One of these simple machines, the wheel and axle, increases our ability to lift heavy items or to move them from one place to another. The wheel and axle uses the mechanics of effort, resistance, speed and force. The earliest known wheel and axle was used in Mesopotamia around the year 3500 BC. It has come to be used in all kinds of modern day inventions from wheelbarrows to cranes.
Wheel and Axle Parts
The wheel and axle consists of two curved part, one large and one small. The larger curved part is the wheel which spins around the smaller curved part - the axle or rod. The axle acts like a fulcrum (a hinge or a pivot point) which spins the wheel.
Examples of the Wheel and Axle
There are a huge number of examples of the wheel and axle in use today. They include:
· egg beaters
· water wheels used in mills
· paddle wheels used on paddle wheel boats
· automobile wheels
· wagon wheels
· Ferris Wheels
· rollers skates and roller blades
· rolling pins
· electric fans
· train car trucks (the wheels)
· record player tables
· Lazy Susans
· water wells
· drawer rails
· machine gears
See some pictures of a few of these wheel and axle examples at:
· My Kids: Examples of Wheels and Axles
How the Wheel and Axle Works
One way a wheel and axle works is by draping a rope, chain, or cable around a grooved wheel - such as a pulley - and using it to lift and lower heavy objects in a vertical direction. An example here would be a crane or a water well. Another way is to rotate the wheel around the fulcrum (a.k.a. the axle) to make the object move horizontally. An example of this would be any type of vehicle. The effort and force can either be applied to the wheel (as with a doorknob or the wheel on the water well) or to the axle (e.g. car tires or machine gears).
In mechanical advantage, larger amounts of force applied to the axle makes the wheel move faster - the car or bicycle travels at a faster rate of speed - the wheel and axle are acting as a speed multiplier. Applying force to the wheel so that it moves a longer distance, creates a large force on the axle so that it turns only a smaller distance. In this case, the wheel and axle act as a force multiplier (i.e. windmill, spindle, water well).
A mathematical equation is used to find the mechanical advantage of any wheel and axle set up. That equation is:
wheel radius (or load) ÷ axle radius (or effort) = M.A. (mechanical advantage)
For example, if a bicycle tire has a 24 inch radius, and the axle has a 1.5 inch radius, then the equation would look like this:
24 inches ÷ 1.5 inches = 16
Mechanical advantage is not measured in units, because the effort and the load are both forces. so the equation is essentially dividing a force by a force. Since the two forces cancel each other out, the mechanical advantage is simply listed as a number.
Science J-Rank. Simple Machines, Wheel and Axle.
Oracle Think Quest. The Wacky Wheel and Axle.
Swirk Interactive Schooling. Wheel and Axle.
Education. Explore Wheels and Axles.
Pinewood Derby. Pro Wheel and Axle Alignment Tool.
Hot Chalk Lesson Plan Page. Simple Machines, Wheel and Axle.