how to build a solar balloon a science with bobert video short

Convection can also be used to make a solar hot air balloon. Dr. Smith is making a single tube out of three garbage bags. He cut the closed end of the center bag then taped the seams of all the bags together using clear tape. He then cut a slit in one corner that was large enough to fit the end of a hair dryer through. After filling the garbage bag balloon with hot air he tied the end with fishing line and waited….and waited…..and waited….for the balloon to take off. It never did….but good try Dr. Smith. If you are going to try this, make sure you use the twist tie and thinnest black garbage bags you can find. The more light you can see through with a flashlight the thinner the bag!

review
Lets review
Density is the mass of an object divided by its volume.
Objects float or sink depending on whether the density of the object is less than or greater than the density of what the object is immersed in.
Hot gas rising is referred to as convection and occurs because the warmer a gas is the more volume it takes up thereby greatly decreasing its density causing it to rise and be replaced by cooler more dense gas
Have you heard the term “warm air rises?” A warmer gas takes up more space than a cooler gas of the same mass. Since the warmer the gas the larger its volume, then the warmer a gas the LOWER its density! Therefore warm gases always rise because they are surrounded by more dense cooler gases. The process of rising warm air is called convection. We can observe convection if you place a wet quarter on an empty cold glass bottle that was placed in a freezer. As the warm air expands and rises it makes the quarter bounce on the bottle. If you place your hands on the bottle you greatly increase convection and therefore increase the rate of the quarter bouncing on the bottle.

Remember those microscopic air pockets we mentioned that were present in a bar of ivory soap? The air in those microscopic pockets should expand if we heat the bar of ivory soap, right? What would happen if we place a bar of ivory soap in a microwave oven and turn it on? Let’s try it. ……as the bar of ivory soap is heated, the air pockets expand and continue to expand…the warmer the air the more volume it requires so as the air pockets get hotter they get larger and larger………let’s turn off the microwave and see just how hot and how soft the bar has become. It is pretty warm but really soft to the touch!



Convection can be used for other things besides making quarters bounce and Ivory soap bars expand. It can be used to make a convection engine. Dr. Smith is cutting out a spiral that you can draw yourself or find on the internet. He then sticks a wood skewar in a candle to hold the spiral over a candle flame. This looks like a disaster waiting to happen Dr. Smith. …..IT works! I told you so!