Riding in a hot air balloon has been a lifelong dream of mine ever since I watched the American Girl movie called Saige Paints the Sky. At the end of the movie, Saige and her friends designed different hot air balloons and rode on them. How does something so huge lift itself off the ground?
Density is equal to mass divided by volume. Mass is easily confused with weight, but they are not the same. Mass is the amount of matter in an object. Weight is the gravitational force on an object. Your mass on Earth is the same as your mass on the moon. But your weight on the Earth is six times your weight on the moon.
The area of a square is one side squared. The area of a rectangle is its length times its width. The area of a triangle is half times its base times height. When we are finding the area of something, we are finding how many squares of a unit can fit inside it. Therefore, an area’s units are squared. With volume, we are looking at how many cubes can fit inside a three-dimensional object. The SI unit for mass is kilogram and the SI unit for volume is cubic meter. Since density is mass divided by volume, its SI unit is kilograms per cubic meter.
We hear about energy a lot. In scientific terms, energy is the ability to do work. Work, in science, is described as using force to move an object. In science class, when we learned about energy, we learned about potential energy and kinetic energy. Potential energy is when an object is not moving, but it had the potential to move. Kinetic energy is when an object is moving. So, at the top of a curve on a roller coaster, the people who are riding the roller coaster will have potential energy. When they are going down a slope, they will have kinetic energy.
The molecules in every single object have kinetic energy. The average kinetic energy of the molecules in an object is what we call the temperature (measured in Fahrenheit in America) of the object. Heat is the transfer of this energy from one object to another. Let’s say you touch a hot iron. What happened when you touched the iron was that the high kinetic energy (which corresponds to high temperature) transferred to the low kinetic energy of your hand. So, when we are “cold,” we actually have a low average kinetic energy.
Hot air rises because it has more energy, which leads to higher kinetic energy (because an increase in temperature — the measure of average kinetic energy — means higher kinetic energy) which leads to more expansion to make room for all these particles that are now flying around at high speed. This expansion leads to fewer molecules in more space. Having fewer molecules in more space describes density. More space corresponds to the volume and fewer molecules correspond to the mass. Remember that density is mass divided by volume. So, if the numerator is small and the denominator is bigger, the overall density should also be small. If hot air has a smaller density than the cooler air around it, it will rise above it.
In a hot air balloon, there is something called the burner. When the burner is switched on, it heats the air particles inside the balloon, making them less dense than the air outside of the balloon, and boom, the hot air balloon floats. To get the hot air balloon back on the ground, the flap at the top of the balloon has to be lifted to release the warm air and make the particles inside the balloon the same density or a greater density than the air around the balloon.
Vaageesha Das is a junior at Morgantown High School.
Today’s information comes from:
- Gainey, C. (2019, August 16). Racing toward Absolute Zero. Retrieved November 10, 2020, from https://blogs.scientificamerican.com/observations/racing-toward-absolute-zero/;
- How Does a Hot Air Balloon Work. (2019). Retrieved November 10, 2020, from https://napavalleyballoons.com/how-does-a-hot-air-balloon-work.php;
- Thermodynamics facts for kids. (2020, October 21). Retrieved November 10, 2020, from https://kids.kiddle.co/Thermodynamics
