An equation is usually used to find the volume of a regular object, such as a cube or sphere; for those with irregular shapes, such as a vine or a stone, a more creative approach is required. Fortunately, there is a very simple method that allows you to find the volume by looking at the water level in a graduated cylinder.
Steps
Part 1 of 3: Measuring the Starting Level
Step 1. Pour the water into a graduated cylinder
Choose one that can easily accommodate the object in question and tilt it as you add the liquid, to minimize the number of bubbles; pour enough of it to reach the mark in the middle of the graduated scale.
Step 2. Look at the level of the meniscus
You can see that the water column is slightly higher near the walls of the container and lower in the center. This concavity is known as the "meniscus" and is the reference point for measuring the water level. Check that the cylinder is on a flat and level surface and that there are no bubbles in the water; carefully observe which notch the meniscus corresponds to.
Step 3. Write down the value
It is important to know the exact starting level; write it down in a lab notebook or table. The value must be expressed in milliliters (ml).
Part 2 of 3: Measuring the Final Level
Step 1. Immerse the object
Slowly insert it into the water until it is completely submerged; if there is not enough water for this to happen, you have to start over by filling the graduated cylinder more.
Step 2. Take the new measurement
Leave the object in the container and wait for the water to settle. Make sure the cylinder is on a flat surface and look at the liquid level again (always referring to the meniscus); the water column should be higher.
Step 3. Write down the measured data
The final level is as important as the first to perform the necessary calculations and must also be very precise; report it in the table or in the notebook expressing the value in milliliters (ml).
Part 3 of 3: Calculate the Volume of the Object
Step 1. Understand the values
Some people jump to the conclusion that the final reading matches the volume of the object, but this is a mistake. This datum represents the sum between the volume of the water and that of the immersed body. You have to calculate the difference between the final and the initial level to get the information you want.
Step 2. Solve the difference
You need to set up the following equation: V.total - Vwater = Vobject. V.total is the final measurement, V.water is the initial one and Vobject is the desired data.
Step 3. Analyze the solution
Make sure the result makes sense; of course, you can check the operations with a calculator. Some clear clues that you have made a mistake are a volume with a negative sign (not physically possible) or a volume greater than the capacity of the cylinder (you cannot measure a body with a volume equal to 30ml in a container with a capacity of 25 ml). If the solution seems wrong, you should first check the math steps, to make sure you have not made any mistakes; if they are correct, you must repeat the experiment and take new measurements.
- If you have found a negative volume, it is likely that you have swapped the subtract for the minuend and there is no need to repeat the experiment.
- If you have obtained a value that is too large to be realistic, you may have made an arithmetic error or found some inaccurate measurements; in this second case, repeat the experiment.
Advice
- Make sure you measure the meniscus accurately.
- Measure the volume of different objects and compare the results.
