A ferrofluid is a special liquid with tiny magnetic particles floating around inside. Since these particles are attracted to each other, they must be coated with a special substance that prevents them from sticking together (so that the ferrofluid remains fluid). What makes ferrofluid so special is that in the presence of an outside magnetic field, each of the tiny particles becomes magnetized and the ferrofluid condenses into a solid.
In this activity you will be able to make and play with your own ferrofluid and see how it behaves in the presence of a magnetic field.
What you’ll need:
- Vegetable oil
- Shallow dish
- Iron filings (from your local hardware store)
- A magnet
What you'll do:
- Pour a bit of vegetable oil into a shallow dish, just enough to make a thin film across the bottom.
- Pour iron filings into the oil and mix the two until they have become a thick, sludge-like material. This is your ferrofluid!
- Use a napkin to absorb any excess oil and allow the ferrofluid to become thicker. A good way to do this is to attach a magnet to the outside of the dish. This will solidify the fluid and let you dab away extra oil.
- Attach a magnet to the dish containing the ferrofluid; the fluid will solidify and take the shape of the magnetic field it is in! Removing the magnetic field will allow the ferrofluid to flow like a liquid again.
- When disposing of your ferrofluid, do not pour it down the drain; this could lead to clogged pipes!
Did you know?
- Ferrofluids are used by the military to coat aircraft; this helps them elude radar.
- Ferrofluid comes to you courtesy of the same folks who brought you Tang and freeze-dried ice cream: NASA scientists! They came up with the idea in order to confine liquids in space.
Watch Ferrofluids in Action!
The pattern that a ferrofluid makes depends on the amount of fluid used, the shape of the container it's in and the strength of the magnetic field used. The movies below were made at the MagLab; the ferrofluid is inside a superconducting magnet with a maximum field about 100,000 times stronger than the Earth’s magnetic field. The movies show a ferrofluid in two different situations:
- Plastic Petri Upsweep. The ferrofluid is in a plastic dish with a slightly convex bottom, so the ferrofluid moves towards the outer edge. As the movie plays, the magnetic field is getting stronger, and the fluid coalesces into smaller and smaller cone-like structures (which you see from the top down).
- Watch Glass Upsweep. The ferrofluid is in a concave dish called a watch glass. The magnetic field is increasing as the movie plays, but is not as strong as in the first movie. As the field gets stronger the fluid, again, forms into smaller and smaller cones, though it's hard to tell them apart toward the end of the movie because of the amount of fluid in the bottom of the watch glass.
What's another word for magnetized?
Answer - Polarized! It's a reference to the north and south poles of the magnet. “Ionize” means to turn an atom into an ion by adding or removing an electron. “Ferrofied” isn’t actually a word – but it sounds pretty cool, doesn’t it?.