# Science 7 Suspected explanations (hypotheses) about the flight of the hot air balloon

Results from each period in finding categories of explanation. The next task will be to develop tests that aim to gather supporting evidence for a hypothesis and challenging evidence for the other competing hypotheses.

Hypotheses / explanations for the flight of the hot air balloon—Period 1

Most common to least

1. When heated the air in the balloon is less dense the air around it and when the overall density of the balloon and the air in it is less than the surrounding air, the balloon floats.
2. When air is heated in the balloon, the pressure inside the balloon increases and when the air is released, the balloon is propelled in the opposite direction. The balloon is a kind of rocket.
3. Upward currents produced by heating the air close to the ground carry the balloon upward. The balloon is carried upward by a convection current.

Rather than offer an explanation, many students invoke a principle or just repeat the observation that when the air in the balloon is heated, it goes up. There seems to be an idea that some substances go up (hot air, gas, evaporated water) against gravity. An explanation of why these things happen is not provided.

Balloon hypotheses period 3

Principle that certain substances OR substances in certain states go up (not really a causal explanation—more of a relation):
A lot of people thought that the air in the balloon makes the balloon float up. That hot air rises or gas goes up or against gravity. Someone else said that because of evaporation, the balloon goes up.
Idea that pressure pushes up or hot air particles push up—may fit in other categories, too.

1. Current of air hypothesis/explanation:
There is a current of air carries the balloon up. Wind, fan, and heated air produce/result in currents.
2. Rocket hypothesis/explanation:
The balloon acts as some kinds of rocket so the air escaping from the mouth of the balloon propels it like a rocket.
3. Density / buoyancy hypothesis / explanation:
When air is heated, it expands. The volume increases while the mass remains constant, thus the density goes down. When the balloon’s overall density is less than that of the surrounding air, the balloon floats.

Period 4 Hypothesis about hot air balloon flight.
1. Hot air is less dense than cold air (Density floating explanation)
2. Hot air increases the pressure inside the balloon when hot air escapes from opening, balloon is propelled like a rocket
3. The heat gun creates a current of air that carries the balloon up.
4. Principle- Hot air rises, and some materials go up

Period5 balloon explanations

Most common to least common

Balloon behaves like a rocket
Hot air has less density then cold air Balloon floats in the more dense air
Hot air “goes up” creates a current/air that carries the balloon up