Demonstrate Archimedes' Principle
Archimedes' principle states that "an immersed body is buoyed up by a force that is equal to the weight of the fluid that it displaces." What does that even mean? Why does anyone care? The science discovered by Archimedes is used to construct massive objects like cruise ships. They can float because they displace as much as they weigh. To clearly demonstrate this principle, start with Step 1.
Steps
- Put a medium bowl inside a large bowl.
- Fill the medium bowl to the brim with water. Don't let it overflow.
- Place a small, floatable wooden object on a gram scale and note the measurement. A building block, a coaster, or a chunk of scrap wood will work provided that it’s small enough to fit in the medium bowl.
- Do not confuse this with a regular scale. Grams are a unit of mass, not weight. Many cheap digital kitchen scales, for example, measure in grams.
- Place the wood in the water. It will float but some of the water will be “displaced” – i.e., will spill into the large bowl.
- Place another, separate container on the gram scale and note the measurement. Leave it on the scale.
- Remove the wood from the medium bowl, then remove the medium bowl from the large bowl. Be very careful not to spill.
- Pour the spilled water from the large bowl into the container on the scale and note the measurement.
- Subtract the mass of the container (Step 5) from the combined mass of the water and the container (Step 7). The result is the mass of the spilled water.
- Compare the mass of the spilled water with the mass of the wood (Step 3). They should be identical.
- Repeat the experiment with a non-floatable object such as a rock. Find its mass, place it in the water, and then compare that with the mass of the displaced water. They will not be the same. Why? Because the rock was too dense to float in the water; in other words, the water didn’t have enough “buoyancy force” (i.e., ability to float an object) to hold up the rock, which sank. Since the object could not remain buoyant, the buoyancy cannot equal the weight of the displaced water.
Tips
- Try the experiment with different objects. Which ones float and which ones sink? Why?
- Be very careful in making sure none of the water overflows into the bigger bowl.
Warnings
- This experiment should be conducted under the supervision of an adult.
Things You'll Need
- Gram scale
- Medium bowl
- Large bowl
- Small piece of wood
- Water
- Graduated cylinder
- Non-floating object (e.g., a rock)
