Sarah floats particles in oil
When you mix solid particles in fluid they usually sink to the bottom, however if you make the particles small enough, instead of sinking they can be suspended inside the fluid.
Using tiny particles (nanoparticles) made from iron oxide particles and putting them in oil so they are suspended rather than sinking, Sarah can use a magnet on the magnetic particles and watch how it acts like a soild even though its a fluid.
Making this fluid (called a ferrofluid) is really easy and you can collect some black sand from one of our west coast beaches, then using a magnet pick select the particles that are magnetic. You can either just suspend these particles in olive oil, or if you have an old coffee grinder you can grind them down so they make smaller particles.
Then put a megnet close to your fluid and watch what happens.