This magic pepper and soap experiment is incredibly easy and fun to do, where kids will learn what happens to the surface tension of water when dish soap is added.


What you’ll need

  • Plate
  • Water
  • Dish soap
  • Black pepper



  • To start, get a plate and fill it with enough water to almost reach the edges, take care to not overflow it.
  • Add a bit of dish soap to a small bowl for kids to dip their fingers into.
  • Sprinkle plenty of pepper on top of the water.
  • Now, let your kids dip their fingers into the dish soap then touch the water in the middle of the plate. As they do this, they will see the pepper move quickly from the centre and group together around the edges.

They will be astounded as the pepper flakes bolt quickly away from their finger to the edges of the plate. It will be interesting to discover what they were expecting to happen at the beginning of the experiment and what they believe happened.

How does it work?

When you add dish soap to water it lowers the surface tension of the water. So in this experiment when the soap is added, the water molecules try to stick together and move away from the soap thereby carrying the pepper flakes with them.

Water molecules are pulled equally in every direction by neighbouring particles, but as the molecules on the surface of the water do not have the same amount of molecules on all sides they are therefore pulled inwards. This causes some internal pressure and forces liquid surfaces to contract to the minimum area.

This demonstration is also a great visual to show kids why they should always wash their hands with soap, using the pepper to represent how soap causes germs to scatter.

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