What You Need:
- A clear, plastic bottle
- Add a small amount of water to the bottle and shake it around so that there is a thin covering of water over the inside of the bottle.
- Light a match and let it burn for a few seconds before blowing it out and dropping it in the bottle.
- Immediately put the cap on.
- Squeeze the bottle a few times.
- A cloud should appear inside the bottle.
The cloud in the bottle forms as a result of the smoke particles from the match and the water inside the bottle. The water combines with the air to form water vapour which is the basis of the cloud. However, the particulates in the smoke are required as they act as nucleation sites to which water droplets can condense and collect on.
Squeezing the bottle increases the pressure inside the bottle which in turn increases the temperature (according to Amontons’ Law of Pressure-Temperature). This causes the water to turn from a visible liquid to an invisible gas hence the cloud disappears. Releasing the pressure therefore causes the cloud to reform.
This is how real clouds form. Water vapour expands and cools as it rises through the atmosphere. There is a limit to the amount of water vapour the air can hold – this value is higher at warmer temperatures. Higher up in the atmosphere where it is cooler and the pressure is lower, the water vapour begins to condense and clouds form just like they did in the bottle when it wasn’t squeezed (i.e. when temperature and pressure were lower). There are plenty of particulates in the air to act as nucleation sites as well.