Balloons and Buoyancy
Links and useful resources
- START HERE: Physics 2024 class outline
- Physics classroom online interactive tools
- OpenSTAX high school physics
- NotebookLM physics notebook
- Physics projects
- AP Physics 1 Dan Fullerton videos
Lesson-specific resource links
- https://www.youtube.com/watch?v=wGRmcvxB_dk
- Ideal Gas Law
- #hw (science) Read 46,000 year old worm revived. 2025-03-03
Lightning Round Questions
- What did Muhammad Ali Pasha do in 19th century Egypt (not the boxer)? (industrialized and modernized many parts of the nation).
- What is the formula for the gravitational force of attraction between any two masses?
- How do you access the command line arguments in a typescript program running on
node? - What does it mean to infer something (especially in a science context)?
- How would you measure the density of an irregularly shaped object?
- What is the purpose of a pull-up or pull-down resistor? How does it work?
Demonstration
Concept summary and connections
- floating and buoyancy
- pressure, temperature, volume
- pv=nrt
- Ideal gas law
- Absolute zero
p = Pressure
v = Volume
n = "amount of material" - usually constant for the problems we're doing
R = Boltzmann constant or ideal gas constant, 8.314
t = temperature in kelvins (the absolute temperature)
Lesson content with examples
We know that temperature is just a statistical property of the energy of motion of the individual particles that make up a substance. In a gas, that motion also shows up as pressure.
Remember temperature?
Temperature is just the way we measure the kinetic energy of the particles that are always rapidly vibrating in all matter. The faster they're moving, the hotter the temperature. But, how do we know that? The answer is that a lot of people did a lot of experiments in reality, but the thing that got us started was looking at the way gases behave as you change their temperatures. Here's the experiment:
- Get a bunch of different gases and put them into a fixed size container with no leaks
- Vary the temperature and measure the pressure for each gas at different temperatures
- If you plot a line through the data for each gas, you'll get a bunch of lines that all cross at -273.15
C, because that is the point at which all motion stops and pressure would therefore be zero!
Absolute zero is the lowest possible temperature for matter, because temperature measures molecular motion, and all motion stops at zero. We can record this temperature in any scale you like:
- In Kelvins, absolute zero is just zero
- In Celsius, absolute zero is at -273.15
C - In Fahrenheit, absolute zero is at -459.67
F
What is pressure, exactly?
Imagine you have a 5 lb weight and you want to use it to make a hole in a board. If you set the weight on the board, it's not going to do the job. Now say you put the weight on the flat part of a thumb tack, do you think you'll have a different result? Why? In both cases, the weight is only putting 5 lbf on the board, so why should the thumb tack penetrate it easily while the weight stops? The answer is pressure - there is a lot more board in the way of the weight than there is in the way of the thumb tack, so the same amount of force is much more concentrated with the tack. Pressure is a way to measure how much force is pushing on a given area rather than in total.
This shows up all the time when we're working with gases and liquids. We talk about the pressure in a pipe, the pressure in your veins, or the pressure of air in a tank. In every case, we're worried more about force per area than total force, because it's the force per area that makes things pop.
Media resources
- Youtube search for "floating and buoyancy"
- Youtube search for "pressure, temperature, volume"
- Youtube search for "pv=nrt"
- Youtube search for "Ideal gas law"