SKILLS
...............................................

How is Density Measured?

Measuring the density of a solid object involves making two different measurements then dividing one of them into the other. First measure mass. That's the easy one. It just requires an accurate balance that measures in grams.


Triple Beam Balance

Next, measure the volume of the object in cubic centimeters. This measurement is more complicated. First there are two different ways to measure volume. If the object is a regular solid (prism, cylinder, sphere, cone) you can measure its dimensions then calculate its volume.

Sphere

4/3pr3

Cube

edge3

Cylinder

pr2h

Rectangular Prism

L x W x H

Cone

1/3pr2h

Pyramid

area of the base * height * 1/3

If the object does not have a regular shape the only way to measure its volume is to use the displacement method.

If the object is small, measure its volume by placing it in a partially filled graduated cylinder and noting the rise in water.

For example: if a graduated cylinder contains 15 mL of water before you add the object, and 21 mL after, the object has a volume of 6 mL. Since one milliliter is equal to one cubic centimeter, the volume of this object can also be expressed as 6 cm3 .


Reading a Graduated Cylinder

If the object is too large to fit into a graduated cylinder what do you do?

Displacement still works but you need a large container with a spout. Fill the container to a level above its spout. Place it on a level surface and allow the excess water to run out. Slowly lower the object into the water and collect all of the water that overflows. (If the object floats, you push it just below the surface of the water and hold it there until the flow of water stops.)


Overflow Can

Measure the volume of water that overflowed by pouring it into a graduated cylinder. Use the graduated cylinder as many times as it takes to measure all of the displaced water.


Copyright 2003-2018 Event-Based Science Institute