A solid as we discussed is made up of molecules that are tightly packed together. A liquid is made up of meolecules that are further apart and can move around more easily and take the shape of what they are in.
The molecules in cornflour (or custard powder that is made of cornflour) can move very close together when they are squashed and act like a solid. When you let go, the molecules move apart and start acting like a liquid which is why the substance can then fall through your fingers. So it is really both a solid and a liquid at the same time! If you fill a whole swimming pool (or even a paddling pool) with cornflour and water you can then walk across the top of it – the pressure of your feet pushing down keeps it solid under your feet. However if you stop walking, the molecules move apart and you sink (like quick sand!). There is a fantastic youtube video showing this, where Richard Hammond from Brainiac walks on custard. Check it out below!
Thanks for your brilliant question, stay curious and see you soon!!
- Lydia from Blast Science