1. BUOYANT FORCE What makes objects float?
Why do some objects float and others sink?

2. Floating & Sinking:
• It’s not just weight!
• It’s not just density!
• Depends on 2 Forces:
– Weight of an object GRAVITY
– BUOYANT FORCE
For example,
aircraft carriers are
80 – 900 tons!
Yet, they float.
For example, much of
an aircraft carrier is
steel which has a
density ~7.9 g/ml.

3. More About Fluids: Floating Science
For solid objects to float, there must be something holding them up.
We know that gravity is pulling down on the object
But what is holding it up?
Gravity

4. As a object sits in a fluid, the particles in the fluid push back on the object
This “pushing
back” is called a
buoyancy force
buoyancy force
Gravity

5. How strong the buoyancy force is depends on the following:
The shape and density of the solid
The density of the fluid

6. What is displacement?
• An object in water, will force water out of the way.
• Moving water out of the way is called displacement.

7. (Think about changing volume!)
Buoyant Force:
Displacing water creates a force
called buoyant force.
Buoyant force = upward push created by
displaced water
Size of buoyant force = weight of water moved
So, changing the amount of water displaced, changes the buoyant force.
(Think about changing volume!)

8. Creating floating objects with materials denser than water:
Buoyancy:
Creating floating objects with materials denser than water:
Change the VOLUME!
Change the MASS.

9. Archimedes Principle Archimedes stated that You can figure out the
Hello
Stevie
Do you like floating?
Archimedes Principle
Archimedes stated that
You can figure out the
Buoyancy force on an object simply by:
Measuring the WEIGHT
of the fluid it displaces
Let’s do it!!!!