How do Clouds Form?
Clouds are like large lakes in the sky. How do they get there? When water from the ground evaporates it rises with warm air. This water, in an invisible gaseous state, is called water vapor. The pressure decreases the higher up in the atmosphere. The air is cooler as well. As the water vapor rises the pressure lowers and the water vapor cools. Eventually the temperature reaches the dew point. This is when the atmosphere is at a temperature in which the air can no longer hold the water vapor, some must condense back to a liquid.
In order to make the change the water vapor needs a non-gaseous surface. This is usually in the form of smoke, dust, ash, or salt in the atmosphere. This is called the condensation nucleus. Think of the tiny particles as cloud seeds. The cooling process allows the water molecules to stick to the dust and each other and creates a cloud. It is visible because of the dust particles. The more water and dust in a cloud the darker it will be. It is amazing to think that a cloud is liquid water floating in the sky.
Lets mimic the process in a bottle.
2 liter bottle
Matches (Teacher Uses)
1. Pour 50 ml of hot water into your bottle.
2. This is the adult step.
We need a little dust. An adult will light a match. Let it burn for a second. Stick it in the opening of the bottle. Blow it out. Hold it in the mouth of the bottle until it stops smoking. Drop the match into the bottle.
3. Quickly screw the fizz keeper tightly on the bottle.
4. Swirl the water around the bottle. Make sure there is no condensation on the sides. We want to see inside the bottle.
5. Pump the fizz keeper 50 times. This can be tricky. You may be able to do less pumps. Some Fizz Keepers are better than others. You may need 60 pumps or more. If the pressure seems to great STOP Pumping. SAFETY FIRST.
6. While watching the center of the bottle, quickly and carefully unscrew the fizz keeper to let the pressure out. It will happen very quickly. Keep your eye on the center of the bottle. You will see a puff of a cloud form. It may go away quickly or stay for a few seconds.
Here is a video I did. The quality may not be the best, but it gives you an idea. I actually pumped 100 times. The fizz keepers I have put a very small amount of gas into the bottle. You will hear the gas released when the bottle is unscrewed. Look closer and you will see the bottle become foggy. If you look by my hand it is much more visible. In a classroom the students will be able to see it well.
What exactly is happening?
The hot water provides the warm air needed to evaporate the water and allow it to rise. The smoke serves as the condensation nucleus. The final thing needed was a change in temperature and pressure. The Fizz Keeper pumps a small amount of air into the soda bottle The more pumps means more molecules in the bottle will collide and compress. This increases the pressure and the temperature. This allows more water to evaporate in the bottle. The bottle is now a high pressure temperature environment.
The real atmosphere is a low pressure and cool environment. To do that the fizz keeper was unscrewed. This immediately releases gas causing the pressure to decrease. The air in the bottle is allowed to expand and the temperature decreases. The water vapor condenses onto the condensation nucleus (smoke and dust) and a cloud quickly becomes visible. This is not exactly like the atmosphere, so in most cases the cloud will not stay long. Make sure to unscrew the fizz keeper quickly and carefully to cause a quick change in pressure.
Lets Investigate Further.
Great for Science Fairs.
Meets the Next Generation Science Standards.