Summer Holiday – Fun Science Activities – Scrumptious Slime & Marshmallow Catalpults

Summer Holiday – Fun Science Activities – Scrumptious Slime & Marshmallow Catalpults

Dr Michelle Dickinson (MNZM) – prize winning nanotechnologist, researcher and educator – has made it her life mission to make science and engineering accessible for all. Her new upcoming book The Kitchen Science Cookbook is packed full of fun ‘recipes’, each teaching an important scientific principle in a format that is perfect for parents and children to enjoy together. Available on Amazon.  Find out more at


 Marshmallow Catapults

Scientific Principle: Energy                           

Time: 30 minutes


Catapults have been used throughout history to launch objects at and over the walls of castles by converting potential energy to kinetic energy. This experiment uses the same theory – but with objects you can eat!

Equipment & Ingredients2 elastic/rubber bands

  • 1 plastic teaspoon
  • Masking tape
  • 7 wooden skewers
  • 5 large marshmallows


  1. Create a triangular base with three of the wooden skewers, joining them with a marshmallow at each corner.
  2. Place one skewer upright into the centre of each of the three marshmallows used in the base, then bring the tips of the skewers together to transform your triangle into a pyramid.
  3. Secure the three skewer tips with an elastic/rubber band, then place a marshmallow over the top.
  4. Use masking tape to attach the spoon to the end of the final skewer.
  5. Feed the spoon-skewer combo through the centre of the pyramid, placing thewooden end into the base triangle marshmallow at the front of the structure and holding the spoon end at the back of the structure.
  6. Place the second rubber band over the top of the pyramid and loop it under the spoon to hold the spoon off the ground or table.
  7. Place a marshmallow on the end of the spoon, pull it backwards against the rubberband and let go!

The Science Behind Marshmallow Catapults

Catapults work by converting energy from one type to another and transferring thisenergy from one object to another. When the spoon is pulled back against the rubber band, energy is added to the catapult system. This energy is stored as potential energy in both the spoon and the rubber band. The further the spoon is pulled back, the more potential energy is stored. When the spoon is released, the potential energy converts to kinetic energy (energy in motion) and the spoon propels forward, releasing the energy stored in it. This energy is transferred from the spoon to the projectile marshmallow sitting in the spoon, and causes the marshmallow to fly through the air. Because the spoon and skewer combo are long and bendy, they act as a lever, pivoting on the marshmallow base and enabling the projectile to be propelled a long way relative to the small amount of effort.

Explore Further

  • What happens if you shorten the length of the spoon-skewer lever? Why do you think that is?
  • Can you construct a catapult using a shape other than a pyramid? How about a square or a rectangle?
  • How does changing the length of the rubber band affect how the marshmallow flies?
  • Can you aim the marshmallow so that it lands in a bowl across the table


Scrumptious Slime 

Scientific Principle: Viscosity Time: ​45 minutes cooking time, 2 hours cooling time 


This slime flows like a liquid but can be rolled like a solid – and the best part is that it’s edible!

Equipment & Ingredients 

  • Saucepan
  • Plastic sandwich bag
  • 395g (14 oz) can sweetened condensed milk
  • 10g (1 Tbsp) cornflour/cornstarch
  • 45ml (3 Tbsp) chocolate syrup


  1. Pour the milk into the saucepan and heat on a low heat.
  2. Slowly stir the cornflour into the warm milk. Continue heating and stirring over a low heat for 20 minutes or until the mixture thickens.
  3. Remove from the heat and stir in the chocolate syrup.
  4. Place in a sandwich bag and refrigerate.
  5. Once cold, roll and squeeze into any slimy shape you want – and watch it flow!

The Science Behind Edible Slime 

Cornflour or cornstarch is a starch made up of long chains of sugar molecules called glucose  which are joined together in a coiled up ball. When exposed to heat and milk, the starch particles absorb water from the milk, causing them to swell. These swollen particles start to press up against each other. This reduces the movement of the liquid, resulting in it thickening or becoming more viscous. Eventually the starch particles burst, freeing up long strands of starch which swell further and absorb the fluid outside the particles. This traps the remaining water in the mixture and turns it into a highly viscous gel or slime. The slime flows like a thick liquid but can be rolled around like a soft solid. The advantage of this recipe is that the slime is edible once you have finished with it!

Explore Further 

  • What edible treats could you add to your slime to add more texture? Does this change the way that it flows?
  • How does the slime flow differently when it is warm compared to when it is cold? Why is this?
  • Can you think of other ingredients you could add, instead of the chocolate sauce, to make different flavoured edible slime?