1. Why does an ice cube float in water?
Buoyant Force
Why does an ice cube float in water?

2. Buoyant Force is the upward force that fluids exert on all matter
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Gravity

3. Buoyant Force and Fluid Pressure
Horizontal pressure is =, so it cancels each other out
Vertical Pressure is the only one that affects
net force
**Water Pressure INCREASES with depth..
This makes pressure on the bottom is
greater than the top

4. Determining Buoyant Force
Archimedes's Principle States: The buoyant force on an object in a fluid is an upward force = to the weight of the fluid the object displaces.

5. Weight versus Buoyant Force
An object sinks if its weight is greater than the buoyant force.
An object floats only when the buoyant force on the object is equal to the objects weight.

6. The rock displaces 5L of water that =50N The rock sinks because
The rock weights 75N
The rock displaces 5L of water that =50N
The rock sinks because
75N > 50N = SINKS

7. The fish weighs 12N
The fish displaces a volume of water that = 12N
12N = 12N = FLOATS

8. The duck displaces a volume of water that =9N The duck floats because
What about the duck??
The duck displaces a volume of water that =9N
The duck floats because
9N = 9N  FLOATS

9. Buoying Up If that duck plunged under water, what would happen?
It would displace more water than it weighed.
The buoyant force would be greater than it’s weight and the duck would “pop” backup. Buoyed up!!

10. More Dense Than Air Why does ice float in water and not in the air?
It is less dense than water and more dense than the air!
Helium is 1/7th the Density of Air!!

11. Math Focus
Ex: Find the density of a rock that has a mass of 10g and a volume of 2cm3
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12. Changing Overall Density
How can a ship of steel, with a density greater than water, float?
Change the shape and this increases the volume.
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13. How can a submarine float and submerge?
Changing Mass
How can a submarine float and submerge?
Ballast Tank –opens to let sea water in which mass, but the volume is the same.

14. Changing Volume
Fish inflate the swim bladder with gases from their blood
*Inflated swim bladder increases the fish’s volume and decreases density= keep fish from sinking
Swim bladder
Most bony fishes have an organ called a swim bladder that allows them to adjust their overall density