1. Topic 3.3 – Density, Temperature and Buoyancy
Mix and Flow of Matter

2. Rainbow Colors
Why did the different substances sit on top of one another?
Each liquid had a different density
The greater densities sank to the bottom.

3. Review We learned that viscosity changes with temperature…. RIGHT?
Does Density change with temperature too???
LET’S FIND OUT TOGETHER!

4. Hydrometers
A hydrometer is a device used for measuring the density of liquids

5. Imagine….
Close your eyes and imagine swimming in a lake on a HOT SUMMER DAY.
Is the temperature of the water the same on the surface as it is when you stretch your legs straight down?

6. The warm water will float on top of the cold water
Warm water has a lower density that cold water!
COOOOL!

7. The Particle Model
The particle model can explain this change in density! WOO!
Particles in a substance move faster when they are heated up
This makes the spaces between the particles larger

8. THIS AFFECTS THE DENSITY OF THE SUBSTANCE!!!
When the spaces get larger between the particles, this increases the volume
BUT the number of particles stay the same
SOOOO…. Warmer liquids will have a lower density!

9. Solids Liquids, Liquids, LIQUIDS… that’s all we EVER talk about!
What about solids? Does the same rules apply to solids?

10. We saw today that solids (coke can and diet coke can) either sink or float.
Do other solids float?
We know others sink… like when you were using displacement to find the density of metal pieces….

12. Buoyant Force Why do some objects float while others sink?
When an object is in a liquid, the force of gravity will pull it down. BUT The liquid has an opposite force called The Buoyant Force

13. Floaters… Objects will float when:
1. The density of the object is LESS THAN the density of the liquid
2. The buoyant force of the liquid on the object is GREATER than the force of gravity pulling it down.

14. Sinkers… Objects will sink when:
1. The density of the object is GREATER than the density of the liquid
2. The force of the gravity acting on the object is GREATER than the buoyant force of the liquid

15. BUOYANCY
Buoyancy is the tendency of an object to float when placed in a fluid.
Buoyant force is the force in fluids that act against gravity.

16. Divers
A diver is able to move down not only because of the gravity force but because of his kicking
Kicking is greater than the buoyancy force

17. A diver is able to move upward because of the buoyant force
Along with the force of kicking
This is greater than the gravitational force of gravity

18. A diver can float suspended in the water
Because the force of gravity and the buoyant force are equal

19. Plimsoll Lines
We know that densities of salt water and fresh water are VERY different…
Can this cause a problem for ships that transport heavy items to a from different places?

20. Ships…
As a ship sails from the Atlantic Ocean (salt water) to the St. Lawrence River (fresh water) it SINKS VERY LOW!
WHY?
It sinks because fresh water is less dense than salt water

21. On the sides of ships are Plimsoll Lines
It shows how heavily a ship can be loaded in different water conditions.

22. WNA = winter north Atlantic
W = winter salt water
S = summer salt water
T = tropical salt water
F = Fresh water
TP = Tropical fresh water