A ghoul has come into your house. You already know that ghouls die when they touch water. Frighten the ghoul away by threatening to drown him.
What you need
• large glass
• saucer or plate or similar
What you do
- Push the centre of the handkerchief into the glass, so that the edges are hanging over the outside of the rim of the glass.
- Pour water into the glass, through the loose handkerchief. Make sure that your audience can see the water easily passing through the handkerchief into the glass. Keep pouring the water until the glass is roughly half full.
- Pull the corners of the handkerchief so that the material is taut over the top of the glass. Hold the glass and handkerchief so that the material stays tightly stretched over the opening. For younger audiences you may like to say some ‘magic words’ that make the hanky water proof.
- Place the saucer or plate on the top of the glass and tip it all upside down, being careful to keep the handkerchief pulled tight.
- Hold the upside-down glass and saucer or plate over the ghoul’s head, making sure that the glass is vertical and the handkerchief is tight. Remove the saucer or plate. The ghoul will be afraid of getting drowned and run away, but your mother will be happy because the water stays inside the glass!
This demonstration is based on surface tension. When the handkerchief is loose, the water can pour through the gaps in the fabric. However, when the handkerchief is pulled tight, the water molecules can form a single surface or membrane across the handkerchief. The surface tension of this membrane is sufficient to overcome gravity.
Tips for Success
Don’t try to substitute a paper tissue for the handkerchief as it won’t work! If the glass isn’t held vertically, some water may dribble out where the membrane attaches to the edge of the glass.