Science

Squishy Circuits

by dontregartha September 28, 2017

Learning outcomes

You will be able to:

  • Construct a simple electrical circuit.
  • Describe the properties of insulating and conductive dough and their purpose in the circuit.

You will need (per group of 4):

  • 1 x Gratnells shallow (F1) tray with lid
  • 2 x Gratnells mini trays or one 4 section tray insert (optional, for organising equipment)
  • 1 x Ball of insulating dough (see recipe and method below)
  • 1 x Ball of conductive dough (see recipe and method below)
  • 1 x 9V PP9 battery
  • 5 x Different coloured LEDs (plus a few spares kept to one side)
  • 2 x Electrical circuit wires with crocodile clips at each end (often black and red but don’t need to be)

For preparation (per class):

  • 1 x Microwaveable container with lid
  • 1 x Shallow Gratnells (F1) or Art (A1) Tray
  • 2 x Large resealable food storage bags
  • 1 x Wooden spoon
  • The dough ingredients (see recipe and method below)

This activity also works for individuals or smaller teams, simply increase the amount of time allocated to complete it. This activity can be repeated multiple times, reusing the same equipment for each team or set up as a full class activity.

Preparation:

  • The method for making the two doughs can be found below. Use food colouring in the conductive dough to ensure the two doughs are distinct and reduce the risk of mixing them during use, or, omit the dye and challenge the students to identify the doughs themselves.
  • Place a ball of each dough, the battery, LED’s and electrical wires into the shallow Gratnells (F1) tray.
  • Use the mini trays or a tray insert to help keep the wires and LEDs tidy and organised if desired.

Dough recipes (sufficient to make enough dough for up to 8 groups):

Conductive dough recipe

  • 1 cup plain flour
  • 1 cup water
  • ½ cup salt
  • 1 tbsp. vegetable oil
  • 4 tbsp. lemon juice
  • Food colouring

Conductive dough method

Add all the ingredients for the conductive dough to a microwaveable container and mix well with a wooden spoon. Heat for 1 min 30 sec. Stir. Heat for 1 min. Stir. Heat for 30 seconds at a time, stirring in between, until it forms into a solid ball of dough. The dough gets hot so do not touch it until it has cooled down enough to handle. Once cooled, knead the dough, using a shallow or art tray to protect the surface, until it forms a smooth ball and place into a sealed, airtight bag until needed to prevent it drying out.

Insulating dough recipe

  • 1½ cup of plain flour
  • ½ cup of sugar
  • 3 tbsp. vegetable oil
  • ½ cup deionized water (distilled or regular tap water can be used but the resistance of the dough will be lower)

Insulating dough method

Set aside ½ a cup flour to be used later. Add the remaining flour, sugar and oil to the microwaveable container and mix well with the spoon. Add ~1 tbsp. of water and mix until it is absorbed. Repeat this step until large sandy lumps begin to form. Turn the dough out into a shallow or art tray and gather into a single lump using your hands. Add small, incremental, amounts of flour or water and knead until you achieve a pliable, dough-like consistency. Place the finished dough into a separate sealed, airtight bag until needed.

If you are not using the doughs straight away, store in the fridge for up to one week. Place in the freezer if you wish to keep the dough for a longer period. Add more flour if the dough gets wetter during storage. Kneed after defrosting at room temperature to restore pliability. Many thanks to Chantelle Lawrence and the technical team at the National STEM Learning Centre for sharing their conductive dough recipe and method. The insulating dough recipe and method is from squishycircuitsTM.

What to do:

This activity can also be run as a team challenge as part of an activity carousel. See Secondary Squishy Circuits for an alternative set of ‘What to do’ instructions. Take a look at our Squishy Circuits video for a demonstration of the below method.

  • Pinch off a piece of conductive dough around the size of a large marble, first roll into a smooth ball in your hand and then into a sausage shape around 6cm long. Place it down in the middle of a shallow tray.
  • Repeat this procedure to make a second, identical, sausage of conductive dough and place it down in the tray parallel to the first leaving a small gap between the two.
  • Pinch off a piece of insulating dough around the size of a large marble, first roll into a smooth ball in your hand and then into a sausage shape around 6cm long. Place it down in the gap between the two lines of conductive dough.
  • Choose which side of your circuit you want to be positive and which you want to be negative. In the video, the right-hand side is positive and the left is negative.
  • Look carefully at your LEDs, one leg is slightly longer than the other. The longer leg is the positive leg. Split the legs of your LED so they are far enough apart to span the gap between the two rows of conductive dough. Put the long leg into the positive (right) side of the dough and the short leg into the negative (left) side.
  • Clip a wire to the positive point on the battery pack and clip the other end (or squish it into) to the positive (right) side of the dough.
  • Clip a second wire to the negative point on the battery pack and clip the other end to the negative (left) side of the dough.
  • Your parallel circuit is formed and the LEDs should light up.

What is happening?

Conductive dough allows the electrical current to flow through it, producing a circuit. If the two sides of conductive dough touch, a short circuit is created and the LEDs will go out. The conductive dough has a much lower electrical resistance than the LEDs. In a short circuit, the electricity follows the path of least resistance, flowing through the dough, bypassing the more resistive LEDs. The insulating dough does not allow electrical current to flow through it, it can be used to isolate different areas of a circuit to stop them from touching. Resistance is a measurement of how insulating something is, the insulating dough is resistive, which means little electricity can flow through it. When the insulating dough is used to separate the two sides of the circuit, the path of least resistance is through the LEDs.

The conductive dough is made with salty water, which conducts electricity. The insulating dough is made with sugary water, which does not.

Other things to try…

  • What happens if you swap the doughs around? Why?
  • Can you make a longer, more complex circuit?
  • Can you add in a buzzer or a motor to your circuit?
  • Can you make a series circuit?
  • Can you make an open circuit and add in a switch using another conductive material to close it?
  • Develop this activity into a STEAM Challenge. Can you make a circuit in the shape of a Christmas tree, star or snail? Use different coloured food colouring in your recipes to create the desired look.
  • Here’s a handy link to instructions to make different types of circuits, or get really creative and make a car, cat or robot!

Health & Safety

As with all Gratnells Learning Rooms What’s In My Tray activities, you should carry out your own risk assessment prior to undertaking any of the activities or demonstrations. In particular, participants should be advised not to connect a LED directly to the battery using the wires/clips as it will ‘pop’, the LEDs should only be connected via the dough.