Lab Tips in Properties of Matter
Water Volume Displacement Method Lab
The ancient Greek mathematician, Archimedes, might be most famous for running naked down the street after solving a tricky problem shouting, "Eureka! Eureka! (I have it! I have it!)" In addition to this awesome phrase, he also contributed much to science.1
Archimedes was is name, and hydrostatics was his game. Hydrostatics is the study of how fluids behave. He also wrote bunches of books on the properties of solids. In fact, one of the experiments he developed is a perfect do-it-yourself laboratory experiment.
The super stylin' Archimedes. (Image from here.)
Still wondering what was so exciting that caused our friend Archimedes to run around naked while screaming "Eureka"? We love a good story, and in case you haven't heard it, here's the low-down. King Hiero II of Syracuse commissioned a goldsmith to create him a crown from a lump of gold. When he received this pricey loot he suspected that the smith had tried to rip him off by replacing some of the gold with the much cheaper silver.2
The King asked his old bud, Archimedes, to devise a way to find out if a gold-silver switch-a-roo had actually occurred. Archimedes racked his brain and must have gotten so stressed over the issue that he decided to take a nice relaxing bath. As legend has it, the answer came to him as he lowered himself into the bathtub and observed the change in water level. The rest is history as the scientist jumped out of the tub and took to the streets yelling in excitement. Eureka.
Archimedes in the tub. (Image from here.)
Archimedes realized that an object immersed in water always displaced a volume of water equal to its own volume. This formed the basis of his "water volume displacement experiment" because he understood that if he divided the weight of an object by the volume of water displaced, he would know its density.
For his experiment, he weighed the crown, a block of gold, and a block of silver. He then immersed each in water, carefully measuring how much water was displaced. He calculated that the crown was less dense than gold but denser than the silver, indicating that the King was right! The crown was a mixture of both metals. Off with the smith's head!
All this fuss over a crown? (Image from here.)
Let's recreate Archimedes' water displacement experiments. We'll need:
- A graduated measuring jug or cylinder
- Three similarly sized objects that will fit in the jug made of differing materials (like limestone, granite, brick, wood, glass, metal, or so on)
- A kitchen scale
Let's do this thing.
- Weigh the three objects individually on the kitchen scale. Hint: If you would like to skip additional conversions down the road, ask the scale to give you a weight in grams.
- Pour water into the jug, making sure that there is enough room to add the object without spilling water.
- Record the volume of water before adding any additional object into the container.
- Immerse one of the objects in the water. Hint: If you've picked a tricky object that floats, you'll have to push it gently under the water with your finger.
- Measure and record the new volume of water.
- Remove the object and repeat the process with the other two objects.
- For each object, you can now calculate the density. Remember density = mass / volume. For example, if a block of wood weighs 6 grams and displaces 8 milliliters of water it's density is 6 g / 8 ml = 0.75 g/ml.
That's all she wrote. Now think about the results. Can you understand and explain how Archimedes was able to prove the goldsmith was a crook?
Here are some videos to watch if you can't get enough of Archimedes.