Astronauts, hospitals, and you depend upon centrifugation all of the time! This lesson will explain how centrifugation works and then will discuss some uses of the centrifuge. Following your exploration of that information, you can test your knowledge with a quiz.

## Centrifugation Definition

Have you ever wondered how they separate skim milk from whole milk? Or how your washing machine is able to get the majority of water out of your clothes? Or how, during a blood test, the hospital is able to separate out the different pieces that make up your blood?

Well, the answer to all of these life mysteries is one and the same. Centrifugation is the process where a mixture is separated through spinning. It is used to separate skim milk from whole milk, water from your clothes, and blood cells from your blood plasma. Although centrifugation is primarily used to separate mixtures, it is also used to test the effects of gravity on people and objects. We’ll delve into all of this later in the lesson, but let’s start by discussing how centrifugation works.

## How Centrifugation Works

Imagine a mixture where there are two different-sized particles. If you left this mixture out, over time the larger particles would settle to the bottom. Unfortunately, this can take a long time.

Centrifugation uses a centrifuge, or a device that can rapidly spin, to speed up this process. Imagine we put the mixture into test tubes, and those tubes into the centrifuge. The centrifuge holds the top of the tubes, and the bottom is allowed to angle out. As it spins, the larger particles would get flung out farther, and smaller particles would stay close to the center.

Why, you ask? Think about when you’re driving in a car and have stuff on your dashboard. If you take a corner too fast, all of the stuff on the dashboard falls off. This is because the objects want to keep following their original path, even when the car turns. So the objects on your dashboard continue going straight, even after the car turns and causes them to fall off.

So, back to our mixture. The centrifuge is spinning, but the particles in the mixture want to keep going straight, so they get flung outward. The larger the particle, the farther it gets flung. This is why the larger particles get flung further out than the smaller particles. So because the particles end up in different places in the centrifuge, your mixture gets separated.

## Uses and Types of Centrifugation

Let’s take a moment to explore the uses of centrifugation in more detail, starting with the whole milk.

• If left alone, the fat (cream) in whole milk will separate from the liquid on its own, but centrifugation is often used to speed up the process. As the milk spins in the centrifuge, the heavier cream spins further out and is captured in separate containers.
• What about your wet jeans in the washing machine? When your washing machine is on the spin cycle, it causes the water droplets to be forced outward into the small holes in the side of your washing machine.
• Finally, when you get your blood drawn at the hospital, they must separate out its components like the red blood cells, white blood cells, and platelets from the plasma. The blood is placed in a tube inside of a centrifuge. As the blood spins, the heavier particles go to the bottom and the lighter particles go to the top.

What other uses do centrifuges have? As you might imagine, they are quite useful in the laboratory where they are used to separate pieces of cells or to isolate DNA. But there’s also more.

Believe it or not, centrifuges can be used to make nuclear weapons. For example, the uranium centrifuge is used to separate out the two forms of uranium you get when you extract uranium ore from the ground. The two forms are called uranium-235 and uranium-238 and, since the uranium-238 is slightly heavier, it gets flung out further in the centrifuge, thus separating out the uranium-235 (which is the form that is needed in weapons).

Let’s not forget the human centrifuge, which is used to train astronauts and fighter pilots and let them experience what increased gravity feels like. Just like the particles we’ve mentioned throughout the lesson, humans would get flung to the outside of the centrifuge and would experience increased gravity.

Finally, centrifuges can be used in geology to test models in order to determine if they are structurally sound. For example, a model of a larger scale structure will be built and then put into a centrifuge to see if it can withstand Earth’s gravity. Geologists can adjust the speed of the centrifuge to simulate different conditions, like a structure on bedrock versus permafrost (frozen ground). This is more efficient than having to build a full-sized structure, and it allows geologists the ability to see how different structures would fare in different types of ground.

## Lesson Summary

Centrifugation is the process of spinning a mixture in order to separate out its components. For starters, centrifugation depends upon a centrifuge, which is a machine that spins, for this process. Centrifuges can be enormous, as is seen with those used to spin humans; or tiny, like those used to separate out blood in labs.

No matter what size, centrifuges work because of some fairly simple physics. Objects, like particles, want to continue down their original path, so when the centrifuge spins, the larger particles continue outward, thus causing them to end up further away from the center of the centrifuge. In other words, the larger the particle, the farther it gets flung, like the fat in the milk separation process, or red blood cells, or Uranium-235, for that matter. This is how a mixture with different sized particles can get separated.

Finally, centrifugation can also be used to test the effects of gravity on people, as is seen with the human centrifuge, or on objects and structures, as is seen in some geology labs.

## Centrifugation: Related Definitions & Uses

• Centrifugation: process whereby a mixture is separated through spinning
• Centrifuge: device that can rapidly spin

Centrifugation is used to separate:

• skim and whole milk
• water from washed clothes
• components of blood at the hospital
• parts of cells/DNA in laboratory tests
• components of uranium ore for nuclear weapons
• simulates increased gravity for astronauts
• tests models of structures to ensure the real structures can withstand gravity

## Learning Outcomes

Ensure your ability to do the following after viewing this lesson on centrifugation:

• Define and analyze the process of centrifugation
• Name several uses for centrifugation