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Winterbourne EarlsChurch of England Primary School

‘As each one does their part, we grow in love’

Understanding the world/ Expressive Art and Design

Science Sparks - exciting science experiments for you to do at home (planned by Mr Sainsbury's Primary Science Trust Team)

Just in case the children needed any more guidance for handwashing tips....(they'll be sick of us telling them!), this is a fun science experiment that my daughter told me about which demonstrates the impact of using soap to wash our hands. Have fun!


Necessary Materials

You only need a few common kitchen ingredients to perform this science magic trick.

  • black pepper (germs)
  • water
  • dishwashing liquid
  • plate or bowl


Steps to Performing the Trick

  1. Pour water into a plate or bowl.
  2. Shake some pepper onto the water's surface.
  3. Dip your finger into the pepper and water.  Nothing much will happen apart from the pepper (or the 'germs') sticking to your finger.
  4. However, if you put a drop of dishwashing liquid on your finger and then dip it into the pepper and water the pepper will rush to the outer edges of the dish.

If you are doing this as a "trick" then you might have one finger that is clean and another finger that you dipped in detergent before performing the trick. You could use a spoon or chopstick if you don't want a soapy finger.

Here's How the Trick Works

When you add detergent to water the surface tension of the water is lowered. Water normally bulges up a bit, like what you see when you look at a water drop. When the ​surface tension is lowered, the water wants to spread out. As the water flattens on the dish, the pepper that is floating on top of the water is carried to the outer edge of the plate as if by magic.