Lifting Lemon

Levitate a slice of lemon using a few simple ingredients found in any pub.

Ingredients:

  • slice of lemon
  • four matches
  • pint glass
  • ashtray
  • water

Instructions

  • Pour water into the ashtray until the water is ~1cm deep.
  • Push three matchsticks into the slice of lemon, in the shape of a triangular pyramid, with the match heads together at the top point of the pyramid.
  • Place the lemon and matchsticks in the centre of the ashtray, so that they float on the water.
  • Light the fourth match and use it to light the other three together.
  • Invert the pint glass over the lemon and matches, letting it sit inside the ashtray.
  • Watch as the lemon slice magically levitates within the pint glass!

How Does it Work?

The simplicity of this trick belies the complexity of the physical processes that contribute to the effect. Firstly, there is a simple air pressure effect caused by the expansion and contraction of the gas within the pint glass as it heats up and cools down. The heat from the three matches causes the air inside the pint glass to get hot. When all the oxygen within the glass is exhausted, the matches go out and the air inside the glass cools down. The cooler air takes up much less space, so water gets sucked up into the glass to take up that extra volume. Secondly, the combustion reaction changes the species present, thereby changing the volume of gas within the glass. When the matches burn they consume the oxygen from the air within the pint glass. The products of this reaction are carbon dioxide and water. The water will be a liquid, thus there will be less gas in the glass, causing the water to be sucked up into the glass to fill the volume.

Tips for Success

The lemon slice needs to be thick enough to support the matches, yet still able to float on the water.

Serving Suggestions

This trick was first developed for use in pubs, and draws on ingredients commonly found in most pubs. However, there's no reason not to use it in other environments also. It is most suitable for demonstrating to small groups of onlookers – it won't attract a crowd by itself, but will maintain the interest of audiences that you are already engaged with.

Did You Know?

This demo is based on the methodology used by Joseph Priestley to demonstrate that oxygen is a component of atmospheric air, and to estimate the proportion of oxygen in the air.