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How to Find Density Using Water Displacement

Published in Density Measurement 3 mins read

To find the density of an object using water displacement, you need to determine its volume by measuring how much water it displaces and then divide its mass by that volume.

Here's a step-by-step guide:

Steps to Determine Density Using Water Displacement

  1. Measure the Mass of the Object: Use a balance or scale to accurately determine the mass of the object you want to find the density of. Record this mass (usually in grams).

  2. Prepare a Graduated Cylinder: Fill a graduated cylinder with enough water to fully submerge the object, but not so much that it will overflow when the object is added.

  3. Record the Initial Water Level: Carefully read and record the initial water level in the graduated cylinder before adding the object. Make sure to read at the bottom of the meniscus (the curved surface of the water). Let's say the initial volume is V1.

  4. Submerge the Object: Gently lower the object into the graduated cylinder, ensuring it is fully submerged. Avoid dropping the object in, as this can cause splashing and inaccurate readings. Also, make sure no air bubbles are trapped on the object.

  5. Record the Final Water Level: Read and record the new water level in the graduated cylinder after the object has been submerged. Again, read at the bottom of the meniscus. Let's say the final volume is V2.

  6. Calculate the Volume of the Object: The volume of the object is equal to the difference between the final water level and the initial water level.

    • Volume of object = V2 - V1

  7. Calculate the Density: Now that you have the mass and volume of the object, you can calculate the density using the following formula:

    • Density = Mass / Volume

    • Density = Mass / (V2 - V1)

  8. Units: Make sure to use consistent units. If the mass is in grams (g) and the volume is in milliliters (mL) or cubic centimeters (cm3), the density will be in grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3). Since 1 mL = 1 cm3, these are numerically equivalent.

Example

Let's say you have a small rock.

  • Mass of rock: 75 grams
  • Initial water level (V1): 50 mL
  • Final water level (V2): 75 mL
  1. Volume of rock: 75 mL - 50 mL = 25 mL
  2. Density of rock: 75 g / 25 mL = 3 g/mL

Therefore, the density of the rock is 3 g/mL.

Important Considerations

  • Accuracy: Read the water levels as accurately as possible to minimize errors.
  • Object Size: Ensure the graduated cylinder is appropriately sized for the object. The object should be fully submerged, but the water level shouldn't exceed the cylinder's capacity.
  • Water Absorption: This method works best for objects that do not absorb water. If the object is porous and absorbs water, the volume measurement will be inaccurate.
  • Meniscus: Always read the volume at the bottom of the meniscus.

By following these steps, you can accurately determine the density of an object using the water displacement method.

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