1. CST Review Session 6
Density
Floating and Sinking
Bouyancy

2. Density...What is it? Mass and Volume
Density is a measure of the amount of matter in a particular volume.
It depends on two things:
Mass
and
Volume

3. How do we Calculate Density?
So, using these two things…
and
We can calculate the density of an object!
Use this density triangle
to figure out the proper
equation.
MASS
Volume m D v

4. Buoyancy
An object placed in a fluid experiences an upward force called BUOYANT FORCE [Bf].
Upward force is greater because of greater pressure = Fluid pressure increases with depth.
Pressure acting at the sides are equal.

5. Fluid Pressure Creates Buoyancy
The deeper you go in the water, the greater the fluid pressure.
Therefore, there is greater pressure on the bottom of an object. This causes the upward force on the object (buoyancy).

6. Archimedes supposedly run out to the street naked!
Archimedes, a Greek Mathematician, studied the force of buoyancy. He came up with this PRINCIPLE: “The BUOYANT FORCE (Bf) acting on an object is equal to the WEIGHT of the fluid DISPLACED by the object.”
Archimedes supposedly run out to the street naked!

7. ILLUSTRATION
The weight of fluid collected is equal to the Bf acting on the object submerged.

8. The WEIGHT of the water the man displaces is equal to the SIZE of the Bf acting on him.

9. KINDS OF BUOYANCY Positive Buoyancy: Neutral Buoyancy:
Negative Buoyancy:

10. How do we know if something will sink or float?
Bouyancy and Density

11. Does SINKING or FLOATING depend on the object’s weight?
NO. It depends on the DENSITIES of the object and the fluid where it is placed.
It is easier to float if the density of the liquid is greater.

12. Floating: The Bottom Line
A substance will float in any liquid if it is less dense than the liquid itself!!
Test 1) Which of the solids will float in olive oil?
Answer: pine and lithium
Test 2) Which of the solids will sink in mercury?
Answer: osmium and gold
Test 3) Which liquids will float in water?
Answer: oil and ethanol

13. Floating Applies to Gases Too!
Test 4) Which of these gases would float in air?
Answer: Helium and Hydrogen
Density (g/mL)     
Hydrogen
Helium
Air
Oxygen
Chlorine