1. Example Lesson:
Buoyancy
Why some objects float
gravity
buoyancy

2. Preliminary Concepts Density = mass / volume -or- ρ = m / V
For example a rock has more mass and thus weighs more than a dinner roll of equal size. h h w w
Which object do you think would be most likely to float in water, the stone or the dinner roll?
This is because the dinner roll is less dense.

3. Archimedes
According to legend… King Hiero II gave a goldsmith an amount of pure gold to construct a crown. After the crown was delivered the king became suspicious that the craftsman had stolen some of the gold and mixed the rest with silver. He asked Archimedes to determine if this was true without melting the crown.

4. Archimedes
While taking a bath, Archimedes noticed that the level of the water in the tub rose as he got in, and realized that this effect could be used to determine the volume of the crown. The submerged crown would displace an amount of water equal to its own volume. By dividing the mass of the crown by the volume of water displaced, the density of the crown could be obtained. This density would be lower than that of gold if cheaper and less dense metals had been added.

5. Archimedes
Archimedes then took to the streets naked, so excited by his discovery that he had forgotten to dress, crying "Eureka!" (meaning "I have found it!"). The test was conducted successfully, proving that silver had indeed been mixed in.

6. = Archimedes Principle
A body immersed in a fluid experiences a buoyant force equal to the weight of the fluid it displaces
Downward force
equal to the weight
of the object =
Upward force
equal to the weight
of the displaced fluid

7. Buoyancy Positively Buoyant Neutrally Buoyant Negatively Buoyant
An object that is less dense than water will float
Neutrally Buoyant
An object that is just as dense as water will float
Negatively Buoyant
An object that is less dense than water will float

8. Buoyancy and ROVs
Typically ROVs used by companies and universities are made to be slightly positively buoyant
Why might this be?
This is so the ROV will float to the surface if it is damaged or communication is broken

9. Buoyancy and Your ROV
Should you make your own ROV positively, negatively, or neutrally buoyant?
What are the advantages and disadvantages of each?
In this setting it is typically best to make an ROV neutrally buoyant

10. - Ballast How to Change Buoyancy + Floats
To increase buoyancy add something that is very positively buoyant like foam
- Ballast
To decrease buoyancy add something that is very negatively buoyant like metal

11. Why Might You Want Both?

12. How to Actively Change Buoyancy
Rises
Sinks
Adding air to a balloon on the ROV makes it rise
Adding water to a tank on the ROV makes it sink

13. Buoyancy Activity
How could we determine the mass of an object without using a scale?
Hints:
The density of water is 1g / mL
This will not work if the object sinks in water
(Archimedes Principle applies to floating objects)

14. Buoyancy Activity See how much water the object displaces
Use the density equation to solve for mass
ρ = m / V (remember ρ stands for density)
(1g / mL) = (mass) / ( volume measured in mL)
(1 g / mL) * ( # mL) = the object’s mass
Check your answer using a scale