Density is defined as it's mass per unit volume. Another way to think of it is as a measurement of how tightly matter is packed together into a defined area. Density is represented by the Ancient Greek letter, ρ, pronounced rho or row. Knowing the density of something will give you an idea of how to predict how two different materials will interact when they are mixed together. For instance, we know that a balloon filled with water will definitely not float – water is more dense than air. However, fill the balloon with helium, and it rises. This is because helium is less dense than air.
Another example from the every day working world is when you have the antifreeze checked in your car. The service technician will pour some antifreeze into a hydrometer. This hydrometer has a few objects in it with different densities. These objects will sink or float, depending on if the chemicals in the antifreeze are still strong enough to retain the freezing point.
Measuring density
Calculating density is relatively straight forward. To calculated density, you need two pieces of information. You need the mass (m) of the item, and the volume (V) of the item. The mass divided by the volume will give you the density of the item. We'll take this in two parts, first telling you how to measure the mass, then how to measure the volume so you can get the density of just about anything.
To measure mass, you'll need a scale. The type of scale you need depends on what you want to find the mass of. If you are measuring something very, very small, you will probably want a micro-balance. If you are measuring something very, very large, you'll need something with a large capacity. For this example, lets assume you want to measure the density of a small rock you found out in your yard.
1. Tare your scale – this is important so you start at zero and get an accurate reading.
2. Place your rock onto the scale surface, and wait a moment. Waiting a moment ensures that the air flowing across the scale is minimal, and number is the most accurate.
3. Write down the mass of your object in grams let's say 5g for this example
That's all you need for the mass!
For volume, you'll need a graduated cylinder, or some other accurate way to measure the level of water. The more accurate the better. For this, we'll use the example of a 100 mL graduated cylinder.
1. Fill the graduated cylinder up to a midpoint line with standard water. You want enough water in the cylinder to submerge the rock, but not so much that when you put the rock into the water that it goes past the point of measurement.
2. Mark down this line – in this example let's use 50mL.
3. Drop in the rock.
4. Mark down the new volume the water is at – Let's say 60mL.
5. Subtract the initial (50mL) from the final (60mL) to get the volume of the rock. In this example, the rock's volume is 10mL.
Now, it's all down to math. The units of measurement for density is kilogram per cubit meter. So, we take our grams and convert them to kilograms to get 0.005kg. Then, we convert our volume in milliliters to cubic meters. Since 1 cubic millimeter is equal to 1 milliliter, it's easy to convert. 10 milliliters is equal to 10 cubic millimeters, and thus we have 0.01m.
All that's left to do is plug the numbers into the formula and solve:
ρ = 0.005kg/0.01m
= 0.5kg/m3
All this applies if you are measuring the density of a liquid or gas, too. If you need help finding the perfect scale and tools for your desnsity experiments, send us a message and we'll help you find the best fit for you.