1. Why do you think the titanic sank?

2. Buoyancy and Buoyant Force
Buoyancy -The ability to float
Acts on a submerged object
Water and other fluids exert an upward force
Acts in the direction opposite to the force of gravity so it makes an object feel lighter.

3. Gravity and Buoyant Force
Weight of a submerged object is a downward force.
Object sinks if pressure is greater
If weight is equal to buoyant force the object will float either partly submerged or totally(depends on weight)
Less weight will float- like a jelly fish; Greater weight will sink

4. Archimedes’ Principle
Mathematician of ancient Greece
States: the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces
For example: suppose your body displaces 50 liters of water in a swimming pool…The buoyant force exerted on you will be equal to the weight of 50 liters of water or about 500 N (newtons)

5. Buoyancy Video

6. What is density?
Density is a comparison of how much matter there is in a certain amount of space.

7. Changing Density
You can make an object sink or float in a fluid by changing density.
Example: ice expands when freezes and occupies more space then liquid water.
Example: helium in a balloon which is less dense then air

8. Density

9. Which one is more dense? Demonstration: People in a square
How about this: Which square is more dense?

10. Which one is more dense?
Now which one is more dense?

11. What is density? Density = mass OR mass ÷ volume. volume
Units for density: g
cm3
ALWAYS REMEMBER UNITS!

12. Let’s try a density problem together
Frank has a paper clip. It has a mass of 9g and a volume of 3cm3. What is its density?
John has an eraser. It has a mass of 3g, and a volume of 1cm3. What is its density?

13. Work on these problems with your neighbor.
Joe has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock?
Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the pen?

14. Now, try these on your own.
Sally has a watch. It has a mass of 4g and a volume of 2cm3. What is the density of the watch?
Mia has a wallet. It has a mass of 15g and a volume of 5cm3. What is the density of the wallet?

15. Liquid Layers
If you pour liquids together that don’t mix and have different densities, they will form liquid layers.
The liquid with the highest density will be on the bottom.
The liquid with the lowest density will be on the top.

16. Liquid Layers-1 Which layer has the highest density?
Which layer has the lowest density?
Imagine that the liquids have the following densities:
10g/cm3. 3g/cm3.
6g/cm3. 5g/cm3.
Which number would go with which layer?

17. Liquid Layers-2 Which liquid has the highest density?
Which liquid has the lowest density?
Which liquid has the middle density?

18. Liquid Layers-3
Imagine that the liquids on the right have the following densities:
15g/cm g/cm3
3g/cm g/cm3
7g/cm g/cm3
Match the colors to the correct densities.
3g/cm3
7g/cm3
9g/cm3
10g/cm3
12g/cm3
15g/cm3

19. Review What is the formula for density?
What happens if you pour together liquids that have different densities?
Will the liquid on the top have the highest or lowest density?
Will the liquid on the bottom have the highest or lowest density?