STEM Box: Ferrofluid (Invented by NASA) (Ages 8 & Up, with Adult Supervision)

Ferrofluid is a liquid (such as water) holding tiny particles of iron compounds that become strongly magnetized in the presence of a magnetic field.  You may ask: why don't the tiny particles ever settle out of the liquid to the bottom?  The answer is that the particles are submicron size (i.e., nanoscale) so that the surface area of each particle is extremely large in relation to its mass. Because of the small particle size and large surface area, the particles attract and hold the molecules of liquid (such as water) by surface tension and/or "adsorption", thereby assuring that the magnetized particles cannot settle out of the liquid.

Ferrofluid was invented by NASA in 1963 (using rocket fuel as the liquid) as a way of ensuring that the rocket fuel otherwise "floating around" inside a tank in a weightless environment could be drawn toward a pump inlet by applying a magnetic field.

STEM Box includes:

(1) 200ml Glass Travel Flask filled with 2.9 grams of Ferrofluid, plus 150ml water* (hand-made)

(2) 1" length x 1/2" diameter cylinder nickel-plated N52 neodymium axially magnetized rare earth magnet (18.1 lbs pull force) in a wooden holder (hand-made)

* We deliberately leave air inside to reduce the risk of breakage if/when the bottle freezes

We found that a strong magnet combined with about 2.9 grams of Ferrofluid (both included) seems to yield consistently beautiful results (i.e., adding more ferrofluid is unhelpful).

Recommended for Age 8 & Up (with adult supervision)

For more background on magnetite, ferrofluid, and magnetism, check out this Veritasium video from early 2023: