1. Chapter 4.2 Physical Science
Buoyancy
Chapter 4.2
Physical Science

2. Monday, September 26, 2011 Supplies: Pencil and Science Journal
Standards:
8c) buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced
8d) students can predict whether and object will float or sink
9f) Apply simple mathematical relationships to determine a missing quantity in a mathematical expression

3. Warm-up
Find the density of an object if its mass is 143 g and its volume is 13.8 mL.
Calculate the mass of matter with a density of 1.2 g/cm3 and a volume equal to 76 cm3

4. Buoyancy
Mass vs weight

5. Buoyancy is a measure of a force
A force is a push or a pull
Buoyant force is the upward push a fluid exerts on an object that is submerged.
Buoyancy is the measure of a buoyant force

6. Your Own Words
What is buoyant force?
What is buoyancy?

7. Strength of buoyant force
Depends on how much of the object is underwater
As you push a beach ball down into the water, the buoyant force gets stronger

8. Imagine this
You are in a swimming pool, with your hands on the edge at the deep end. What happens as you fill your lungs with air? What happens when you exhale the air? Write down your answer. Then compare the answer with your neighbor.

9. Archimedes’ Principle
3rd century, Greek mathematician
Buoyant force is equal to the weight of the fluid displaced by an object

10. Why do things float or sink?
If the buoyant force is greater than an objects weight, it floats. Positive buoyancy
If the buoyant force is less than an objects weight, it sinks. Negative buoyancy.
If the object stays where you place it in the fluid, Neutral buoyancy.

11. What floats List 3 things that float in a pool.
List 3 things that sink to the bottom of a pool.

12. Density and Buoyancy
If you know an objects density, you know if it will sink or float.
Water has a density of 1.00 g/cm3
Consider average density

13. What is a Fluid Buoyancy doesn’t just apply to water.
A fluid is a liquid or a gas.
Heavier gases sink toward the ground

14. Why
Why does a hot air balloon float?
What makes it stop going up?