A photograph of the sound barrier being broken by a US Navy Jet as it crosses the Pacific Ocean at the speed of sound just 75 feet above the water. Condensation of water is caused by the rapid expansion and consequent adiabatic cooling of air parcels induced by the shock (expansion/compression) waves caused by the plane outrunning the sound waves in front of it.

Homemade Clouds in a Bottle

The clouds you see in the sky are formed when water vapor is cooled enough to form tiny water droplets. When moist, cool air rises to a higher altitude, it cools, water droplets are formed, and voila – you have clouds. In this experiment we’ll duplicate this same process by causing air in a bottle to rapidly cool.

  1. Put a small amount of water into the jar. Just enough to cover the bottom.
  2. Place the glove into the jar with the fingers pointing down. Stretch the mouth of the glove over the top of the jar.
  3. Carefully insert your hand into the glove being careful not to break the seal. Pull your hand (with the glove still on it) outward quickly. Make sure you don’t break the seal.
  4. Now remove the glove and drop a lit match into the jar. Quickly put the glove back into the jar and seal it again.
  5. Put your hand back into the glove and quickly pull it outward again.

Surprised! The clouds form when you pull the glove outward and disappear when you put your hand back into the jar.

Water molecules are in the air all around us – they’re just invisible. So we do indeed have some water particles in the jar. When you pull the glove outwards you make more room in the jar and the air in the jar hence has more room to expand. This process causes the air and water particles in the jar to cool slightly. When the air cools, the water particles begin sticking to each other (just like the formation of clouds).

The match adds another component to this mix – smoke particles, which are solid. Water particles will bunch together more easily if there are some solid particles around to act as a nucleus. The smoke particles serve this purpose well and hence facilitate the formation of the ‘clouds’.

When you put your hand back into the jar you compress the air which has the opposite affect of expansion – the air heats up. This may seem a little confusing but just remember expansion causes cooling and compression causes heating.

Parent/Teacher/Advanced Notes

Clouds form from water that has evaporated from lakes, oceans, and rivers, or from moist soil and plants. This evaporated water, called water vapor, expands and cools as it rises into the air. Air can hold only a certain amount of water vapor at any given temperature. Warm air can hold more water vapor than cool air can. When the temperature drops, some of the water vapor begins to condense (change to a liquid) into tiny water droplets.

For water vapor to condense, particles so small they can be seen only through a microscope must be present. These particles, called condensation nuclei, become the centers of the droplets. Many condensation nuclei are tiny salt particles or small particles present in smoke. Most droplets measure from 1/2,500 to 1/250 inch (0.01 to 0.1 millimeter) in diameter.

If the temperature is cold enough, and other conditions are right, water vapor does not condense and form a liquid droplet. Instead, the water vapor turns directly to ice through a process called sublimation. For sublimation to occur at temperatures above -40 °F. (-40 °C), small particles similar to condensation nuclei, with a shape somewhat like an ice crystal, must be present. These particles are called freezing nuclei.

Experiment Supplies

Supplies: Glass jar, Matches, Rubber gloves

Sources: MIT
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