Pouring Treacle

What you need

  • A balloon.
  • A bin bag or old newspaper. In fact, make that several old newspapers...
  • A jar of treacle or pourable honey.

What you do

  1. Cover your table with the bin bag or sheets of newspaper. It wouldn't hurt to cover the floor too, just in case.
  2. Blow the balloon up, and rub it on your hair or something woolly. With a bit of luck, you'll rub some electrons onto the balloon, and it'll become negatively electrically charged.
  3. If you hold the balloon near a gently-running tap, you might just see the stream of water being deflected towards it. Sometimes this works rather well, but even so, it's not terribly exciting. Which is where the treacle comes in...
  4. Hold the treacle jar high above the newspaper, and tip it so a very gentle stream of treacle drizzles out. Now, very carefully, bring the charged balloon near the flowing treacle.
  5. You should see the stream of treacle bending right around the balloon. With a little practice, it's possible to make the treacle flow sideways and even slightly upwards, but you'll need a very steady hand. And yet more sheets of newspaper to catch the drips.

What's going on?

The balloon is made of rubber and is a great insulator: it does not let charges move around freely on its surface. When you rub the balloon, electrons which have previously been orbiting hair atoms are physically rubbed off and added to the surface of the balloon. The result is a small patch on the balloon which is negatively charged.

The treacle is a neutral: it doesn't have any excess positive or negative charges. However, the molecules that make up the treacle are polar: although neutral overall, each molecule has a positive and a negative 'side'.

When the negative balloon approaches the flow of treacle the molecules twist with their positive side facing the negative balloon. Since opposite charges attract the treacle moves towards the balloon. And because the treacle is so thick its slow motion allows the molecules to spend longer in the electric field, the treacle moves more than a thinner, faster moving liquid such as water.

The treacle will flow sideways and in some cases even upwards. It is interesting to note that only a charged up balloon can make the treacle defy gravity - showing that the electromagnetic force is considerably stronger than gravity.

Special safety advice

Although perfectly safe, there is a real risk of the treacle pouring onto the floor, and so carpeted rooms are best avoided for this experiment. If you intend to repeat the experiment, try to use a fresh balloon unless you want treacle in your hair.