Have you ever heard that hot air rises? That's true! The moving of warm and cold air causes currents. Air currents are what cause different kinds of weather, like thunderstorms! We can't see the moving air, but do you think colored water might act the same way? Do this experiment to find out! Make sure you have an adult help you with the hot water and the knife.
What You Need:
- Large glass jar or beaker
- Small cup or beaker (it needs to fit inside the jar)
- Food coloring
- Plastic wrap
- Rubber band
- An adult to help
What You Do:
- Ask an adult to fill the small cup or beaker with very hot (almost boiling) water and add several drops of food coloring. Stretch the plastic wrap smoothly over the cup and seal it with the rubber band. (The plastic wrap will puff up--this is because the air above the water is heating up and expanding!)
- Fill the jar almost full with cold water from the tap.
- Use a pair of tongs to set the cup of hot water in the bottom of the jar.
- Have an adult slice open the plastic wrap with the knife and watch what happens to the colored water!
Air is made up of lots of tiny molecules. As air heats up, its molecules start to move faster and farther apart from each other, making the air thinner and lighter. This closeness of molecules to each other is called density. Warm air is less dense than cold air. The warm air floats up through the cooler air, which is heavier and thicker, or more dense. Then, as the warm air rises it starts to cool off and its molecules move more slowly and closer together and it sinks again. This is called convection. When the air moves up and down, it forms currents.
The same thing happens in the jar of water. The hot water is less dense than the cold water surrounding it, so it rises to the top of the jar. What happens as the colored water gets to the top? It stays there for a little while and then moves back down towards the bottom of the jar as it cools down. The colored water starts to mix with the clear water as it cools.
Convection happens in the atmosphere- the layer of air in the sky above the ground. When convection currents happen in the atmosphere, big clouds are formed. Sometimes those clouds turn into thunderstorms. Then, when the warm air cools down again, it starts to sink and breaks up the thunderstorm.
Can You See Static Electricity?
Lightning makes a big streak of light across the sky. In this experiment, you can create a small spark of light that acts similar to lightning, and find out how lightning happens!
What You Need:
- Aluminum pie plate
- Piece of wool (you can use a wool scarf or sweater)
- Styrofoam plate
- Pencil with a good eraser
What You Do:
- Set the pie plate upside down on the table and have an adult push the thumbtack through the center. Pick up the pie plate and turn it over. Push the eraser onto the point of the thumbtack.
- Put the Styrofoam plate upside down on the table and rub the piece of wool back and forth over it very quickly for about a minute.
- Using the pencil as a handle, pick up the pie plate and set it on top of the Styrofoam plate (the plate will stick to it!).
- Touch the pie plate with one finger, making sure that you don't let anything else touch it or the Styrofoam plate before you do.
When you rubbed the wool over the Styrofoam plate, you created static electricity. The Styrofoam plate became covered with negative charges when you rubbed it with the wool. The pie plate had a positive charge, so when you set it on top of the Styrofoam plate, some of the negative charges from the Styrofoam plate were attracted to the positive charges on the pie plate, making the two plates stick together. Then, when you touched the pie plate with your finger, some more of the negative charges "jumped" from the pie plate to your finger because your finger had a positive charge that the negative charges were attracted to. The "jump" happened so fast that all you could see was a tiny spark of light. You probably also felt a small shock and heard a crackling sound. If you didn't see a spark, try doing the experiment again in a dark room (the spark still might be too small to see, though, so you may only be able to hear and feel the static electricity).
Static electricity is the same stuff that makes your hair stand up during a pillow fight or shocks your fingers when you touch a cold door handle. You might also be able to see sparks or hear crackles of static electricity on your bed covers at night. That is because some materials, like fleece or wool, collect static electricity, then the negative and positive charges between your blankets and sheets meet up and make tiny sparks and crackling sounds.
Static electricity is not quite like normal electricity. It can't flow by itself, so it sticks to an object until it can be transferred to something else, like from a pillow to your hair. Since negative and positive charges will always try to get closer to each other, static electricity can sometimes "jump" from one object to another and make a spark. Sometimes the spark will be too small to see, but you can almost always at least hear a crackle. Lightning happens in exactly the same way. Usually, a negative charge from a thundercloud is trying to find a positive charge to meet up with, and it will "jump" from the cloud towards a positive charge on the ground or in another part of the cloud. When it happens, instead of seeing a small spark, you see a big flash of lightning because the charges have more force (they are much stronger) than the static charges in this experiment.