SCI Blog

At the Science Center of Iowa, our goal is to be a quality community resource for informal science learning where children, families, school groups and individuals of all ages come to explore science and technology.

To continue the learning outside our building, we bring you the SCI blog! Our knowledgeable staff, along with special guests and local scientists, will give you a behind-the-scenes look at SCI activities, in-depth information about science events and STEM connections in the Des Moines area.

All Posts

  • Cloud in a Bottle

    Where do clouds come from? How are they made? What are the made of? Check out this video of one of our favorite science demonstrations – the Cloud in a Bottle - and learn how to make your own using the instructions below!


    • 2-liter bottle 
    • Rubbing alcohol 
    • Bicycle pump with rubber stopper (cork works, too) 


    • Fill the 2-liter bottle with about half cup of rubbing alcohol 
    • Wait three minutes for the alcohol to evaporate a little 
    • Insert the rubber stopper into the top of the bottle and pump until you can hardly hold the stopper in the bottle top! 
    • Remove the stopper from the bottle to see what happens! 

    What's going on?

    What did you see happen when the rubber stopper was removed? What did you hear? 

    You probably saw what looks like a cloud instantly form inside the bottle, and you probably heard a loud rush of air as well.  

    Clouds form when individual gas molecules stick together to form tiny liquid droplets. These droplets usually form around some sort of particulate matter, like a small piece of dust. When huge groups of these liquid droplets come together and float, they form a cloud.  

    The clouds in our sky are made of water, but the cloud in the bottle is made of alcohol. The reason we use alcohol is because it evaporates (or turns from liquid to vapor) much more quickly than water.  

    When air is forced into the bottle using the bike pump, the pressure of the gas dramatically increases. As the gas molecules are forced closer together, the temperature increases as well, allowing the air to fit more vapor particles. Once air rushes out, the pressure and temperature dramatically decrease. This change in temperature and pressure forces the vapors to condense into liquid droplets, which creates a visible cloud.  

    How long does it take for the cloud to disperse? What happens to the cloud when you insert the rubber stopper and pump more air back into the bottle? 

    FUN FACT: While Earth’s clouds are made mostly of water, clouds on Jupiter are made of ammonia and methane! What else could clouds be made of? 

  • Cartesian Diver

    The "Cartesian Diver" is a classic science experiment that demonstrates the principle of buoyancy. Here's how you can try it at home!


    • Bottle with cap 
    • Water 
    • Eye dropper (or ketchup packet) 
    • Pitcher 


    • Fill the bottle nearly to the top with water.
    • Fill the pitcher with water.
    • Use the water in the pitcher to fill the eye-dropper. Slowly fill the eye dropper with water until there is enough for it to float just below the surface of the water.
    • Place the eye dropper in the bottle, and screw on its cap.
    • Squeeze the bottle, and observe what happens to the diver.

    The Science 

    So why does the eye dropper fall to the bottom of the bottle when it's squeezed? 

    This experiment demonstrates how density is related to buoyancy, which describes how a liquid will push an object upwards. If the object submerged in the liquid is light enough, the liquid will push that object up. If the object is too heavy for the liquid to push it upward, it will sink. 

    Can you think of anything that can float in water? These things are buoyant!  

    Can you think of anything that sinks in water? Those things are negatively buoyant! 

    As the bottle is squeezed, the pressure inside it increases. As the pressure goes up, the liquid in the bottle pushes harder against the walls of the bottle and all the other molecules in the bottle. 

    You might have noticed that the air bubble inside the eyedropper gets smaller as the bottle gets squeezed. This happens because the increase of pressure on the liquid inside the bottle is compresses the air in the diver.  

    As that air becomes compressed, it becomes denser and too heavy for the water to keep it at the top of the liquid! It becomes negatively buoyant and sinks to the bottom on the bottle.  

    When you stop squeezing on the bottle, the pressure decreases. The air bubble inside the eyedropper expands and becomes less dense. It becomes buoyant again and floats to the top!