Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Centrifuge
SCI-FUN Roadshow Exhibits -- Centrifuge
In this exhibit you learn about how we can separate out cells floating in liquid.

Blood is an example of cells in suspension. This means that cells are floating around in liquid. In blood, red blood cells, white blood cells and platelets are floating in the plasma.

If we leave any suspension out for a while, gravity will cause the different parts of the suspension to form layers, with the heaviest things at the bottom and the lightest at the top.

We can speed up this process using a centrifuge. A centrifuge spins the suspension at high speed. This generates centrifugal force, a force which pushes things away from the point of rotation. Heavy things will end up furthest away from the point of rotation.

Cells in suspension can be separated this way, because they are heavier than the liquid they are floating in. Donated blood is often separated so that different parts of the blood can be given to different patients who need it.

Centrifuges are also used in biology labs which grow cells. Cells are often grown floating in liquid growth media. Cells can be separated from the growth media using a centrifuge. This means that the cells can then be put into new growth media, treated with chemicals or analysed.

Centrifuges in labs can spin tubes around at thousands of rotations per minute. The forces generated are thousands of times the force of gravity. To give you an idea of what that means, when you go on a roller coaster, you sometimes get the experience of being sucked into your seat. The highest force you might experience on a roller coaster is only 5 g, or 5 times gravity.

Centrifuges are also used for nuclear power. Nuclear energy relies on different isotopes of chemicals, that is the same chemical but with different weights. Centrifuges can be used to separate out the different isotopes.

1 Blood is an example of cells in ________.
2 In what order are the layers that form in a suspension?
3 What force is generated in a centrifuge?
4 Why do we separate out donated blood?
5 How are cells often grown in labs?
6 How does the spin cycle on a washing machine act like a centrifuge?

1 Half fill a (small) bucket with water. Go outside and hold the bucket out at arm's length. Spin around, allowing the bucket to swing out to the side. The water will be kept in the bucket by centrifugal force. Now add a bit of sand to the bucket and stir it up. While the sand is still floating about, spin the bucket around again. The sand will now be at the bottom of the bucket.
2 Look for examples of centrifugal force in day-to-day life. For example, long hair moving when a person spins, how a wet dog dries itself or how you move in a car when it turns a corner. Can you spot any other examples?