You will need:
- Food colouring
Mix 50 ml of water to 100g cornflour, and add a few drops of food colouring.
The consistency should let you roll it in your hand into a ball, then drip back into the container when you stop rolling.
You can play with it and experiment. Try punching it, rolling it, pushing it.
The science: Cornflour is made up of lots of tiny starch particles and when it is mixed with water, the starch particles become suspended in liquid as the water moves in between them. The water acts as a lubricant so when you move the mixture slowly, the particles have time to move past each other and the mixture acts like a liquid, and when you apply force, it acts like a solid as the particles lock up.
This is called a non-Newtonian fluid, as it doesn’t obey Newton’s Law of Viscosity - the liquid changes depending on the force you apply to it.
Fun and messy.