Wheel and Axle
A wheel and axle is very similar to another simple machine, a rotating version of a lever similar to a screw. As
the rope winds up on the axle below, it looks very similar to the threads of a screw. The wheel part is the larger
circular object on the end. The axle is a smaller circular object attached to the wheel. Like all simple machines,
the wheel and axle work to reduce the potential energy (PE) we feel when lifting something into the air.
Axle
Wheel
Lift a 200 lbs. bucket high into the air using only your arms. As you can imagine, this would be difficult if not
impossible for lots of people. If we break the 200 lbs. into a more manageable size, say 20 lbs., it would be
rather easy. That’s what a wheel and axle is doing, breaking a larger PE into something more convenient.
Instead of lifting a weight straight into the air feeling the entire PE at once, a wheel and axle is separating it into
smaller chunks to make lifting easier. Even though it makes lifting easier, it does not mean the machine works
faster. In most cases, the work takes longer.
Whenever we talk about how much easier a simple machine makes life, we talk in terms of the machine’s
mechanical advantage (MA). To calculate the MA of a wheel and axle, you divide the diameter of the wheel by
the diameter of the axle. This number tells how much a machine is reducing the potential energy of lifting
something. So if a wheel and axle has a MA of 10, it is reducing the PE 10x.
There are many types of machines that rely on a wheel and axle such as bikes, cars, and lawn mowers to name a
few. All of these use the wheel and axle to make lifting or pulling much easier.
Create a graphic web for a wheel and axle:
Wheel
and Axle
How does a Wheel and Axle work as a simple machine?
1. Using a ruler, measure the diameter of the axle in centimeters.
Diameter
2. Because the left side hook is nearly equal to the size of the axle, we will assume they have the same
diameter.
3. Calculate the predicted mechanical advantage by dividing the hook diameter by the axle diameter.
Diameter of
the axle
Diameter of
the hook
Predicted Mechanical
Advantage
4. Check that the plastic bucket with 1 kilogram weight is attached to the hook on the end of the string.
5. Begin rotating the wheel using the hook on the left side of the wheel and axle a total of 3 complete turns.
Do not let go of the hook or it will spin backwards.
6. Using a meter stick, measure in centimeters the height from the counter up to the bottom of the plastic
bucket. _______________________
7. Carefully, connect a spring scale to the hook. Do not let the bucket drop!
8. Pull down on the hook and try to keep the bucket from moving backwards. Record the weight needed to
keep the bucket from dropping.
Weight in the
bucket
Weight on the
hook
Actual Mechanical
Advantage
9. Carefully ease the bucket back to the counter. Calculate the actual MA by dividing the weight in the bucket
by the weight on the hook.
10. Compare the actual MA to the predicted MA. Are they the similar, the same, or different?
________________________________________________________________________________
11. Using a ruler, measure the diameter of the wheel on the right side in centimeters.
Diameter
12. Calculate the predicted mechanical advantage by dividing the diameter of the wheel by the axle diameter.
Predicted Mechanical
Diameter of the
Diameter of
Advantage
wheel
axle
13. Begin rotating the wheel using the hook on the right side of the wheel and axle a total of 3 complete turns.
Do not let go of the wheel or it will spin backwards.
14. Using a meter stick, measure the height from the counter up to the bottom of the plastic bucket.
_______________________
15. Carefully, connect a spring scale to the hook on the right side wheel. Do not let the bucket drop!
16. Pull down on the hook and try to keep the bucket from moving backwards. Record the weight needed to
keep the bucket from dropping.
Weight in the
bucket
Weight on the
hook
Actual Mechanical
Advantage
17. Carefully ease the bucket back to the counter. Calculate the actual MA by dividing the weight in the bucket
by the weight on the hook.
18. Compare the actual MA to the predicted MA. Are they the similar, the same, or different?
_________________________________________________________________________________
19. Does a larger mechanical advantage give more or less movement of the table? Explain your reasoning.
_______________________________________________________________________________________
_______________________________________________________________________________________
20. Which wheel is easier to turn? Why do you think this is?
_______________________________________________________________________________________
_______________________________________________________________________________________
21. Place the block of wood on top of the sandpaper.
22. Place a 500 gram weight on top of the wood.
23. Have one team member hold the sandpaper and gently pull the wood.
24. How much weight is needed to pull the wood and 500 gram weight across the sandpaper?
25. Repeat steps 21-24 now using the wooden car. How much mass is needed to pull the car across the
sandpaper?
26. To calculate the actual mechanical advantage, divide the weight from the block of wood by the weight from
the car.
Weight in grams without wheels
Car with wheels weight in grams
Actual Mechanical advantage
27. How do wheels make our life easier?
________________________________________________________________________
________________________________________________________________________
Class Examples
Calculate the mechanical advantage of the following machines.
Data Table
Wheel and Axle
Diameter of the wheel
Diameter of the axle
Old fashioned
bike
BMX bike
150 cm
50 cm
2 cm
2 cm
Mechanical advantage
Based on the information gathered from your experiment, which bike would be easier to pedal? Explain your
answer.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Other than a car, bike, or lawn mower, name two different machines that use a wheel and axle to make work
easier.
1.
2.