The water displacement method is a simple way to determine the volume of an irregularly shaped object using Archimedes’ principle. This method can be easily performed using just a ziplock bag and water.
What is Archimedes’ Principle?
Archimedes’ principle states that the buoyant force exerted on a submerged object is equal to the weight of the fluid that is displaced by the object. In other words, the amount of water displaced is equal to the volume of the submerged object. This principle allows us to calculate the volume of an object by measuring the amount of water it displaces.
What You’ll Need
- Ziplock bag (quart or gallon size)
- Water
- Ruler or measuring tape
- Marker
- Container to hold water (bowl, bucket, sink)
Steps
- Fill the container with water. The amount of water needed will depend on the size of the object, but you’ll want enough to fully submerge it.
- Seal the ziplock bag, removing any excess air. You want the bag to lay flat.
- Mark the water level on the outside of the container with a marker. This is your reference point.
- Slowly lower the ziplock bag into the water. The bag will cause the water level to rise. Be careful not to allow any water into the bag.
- Once the bag is fully submerged, mark the new water level on the container. This is the total volume displaced.
- Remove the ziplock bag from the water.
- Measure the difference between the two water levels. This measurement indicates the volume of water displaced, which is equal to the volume of the ziplock bag.
Calculating Volume
To calculate the exact volume displaced in cubic units, you’ll need to measure the dimensions of the container and do some simple math:
- Measure the length and width of the water surface in your container (cm, inches, etc). These are the surface area dimensions.
- Measure the distance between the two marked water levels. This is the height.
- Multiply the surface area by the height to calculate the total volume displaced.
For example, if your container has a surface area of 12 in x 8 in and the height difference was 2 in, then:
Surface area: 12 in x 8 in = 96 sq in
Height: 2 in
Volume displaced: 96 sq in x 2 in = 192 cubic inches
So the total volume displaced by the ziplock bag is 192 cubic inches.
Tips
- Make sure no air bubbles are trapped in the ziplock bag.
- Lower the bag slowly to minimize water splashing.
- For irregularly shaped objects, take multiple volume measurements from different angles and average them.
- Use a rigid container with straight sides to make height measurements easier.
- The more water used, the easier it is to measure small differences in water level.
Real World Applications
The water displacement method using ziplock bags has many practical uses, including:
- Measuring the volume of foods for portioning or recipes.
- Calculating the volume of oddly shaped objects or containers.
- Simple science experiments for kids to learn about volume and displacement.
- Determining volumes for shipping costs or storage capacity.
- Estimating the size of organs or tumors in medical applications.
Experimenting with Different Shaped Objects
The water displacement method can be performed on objects of any shape, not just ziplock bags. To demonstrate how it works for irregular solids:
- Collect several objects of different shapes, such as marbles, pebbles, Lego blocks, clay balls, etc.
- Predict the relative volume of each object (which will displace the most/least water).
- Use the water displacement method to measure the volume of each object.
- Sort the objects from smallest to largest based on the measured volumes.
- Compare your predictions to the actual volumes.
This activity shows that volume is independent of object shape. Students can experiment with different shaped objects and learn how the water displacement method works for irregular solids.
Measuring Volume Change of an Irregular Object
The water displacement method can also demonstrate how the volume of an object changes:
- Take an irregularly shaped object like clay or dough.
- Use the water displacement method to measure its initial volume.
- reshape the object, making it taller, flatter, etc.
- Re-measure the volume using water displacement.
- Continue reshaping the object and taking measurements.
This shows how volume changes when the shape is deformed, even if the mass stays the same. Students can experiment with different shapes and learn about the relationship between volume and shape.
Conclusion
Using the water displacement method with a ziplock bag allows easy and accurate volume measurements of irregular solids. This simple technique relies on Archimedes’ buoyancy principle and can be applied to a variety of practical situations where an object’s volume needs to be determined. With just household materials like plastic bags and water, students can gain hands-on experience and visualize the concepts of volume and displacement.